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Family Liadytidae Ponomarenko, 1977 Diagnosis (modified from Ponomarenko 1992, English translation of Ponomarenko 1977): Medium-sized aquatic beetles with oval, biconvex body. Head noticeably retraced into prothorax, scutellum visible. Mesocoxae located close to each other. Metepisterna reaching mesocoxal cavities. Metaventrite without anteromedial process protruding between mesocoxae, medially with elevated area sharply limited laterally. Anterior margin of metacoxae forming small median emargination bounded in front by extension of transverse metaventral suture. Legs slender and long. Metatibia not shorter than metafemur and metatarsus, very slender, linear. Tarsal segments not broad or paddle-shaped. Tibiae and tarsi with swimming setae. Notes: A broad lateral part of the metathoracic praeepisternum, a metathoracic anepisternum that reaches the mesocoxal cavities, and a transverse suture of the metaventrite characterize only two known families of Dytiscoidea: Liadytidae and Aspidytidae, the only observable difference between which listed by Balke et al. (2003) is the absence of swimming setae in Aspidytidae. This character is, in fact, insufficient for distinguishing between families of Dytiscoidea, because the families Noteridae, Dytiscidae and Coptoclavidae include members that vary in the state of this character. The characters most clearly distinguishing Aspidytidae from the other Dytiscoidea, configuration of the scapus and pedicellus (Ribera et al. 2002), are not discernible in the known species of Liadytidae. The new species Liadytes aspidytoides sp. n. is placed here in Liadytidae, based on the age of the fossils and on their mesocoxae located close to each other and the absence of the anteromedial metaventral process. This character distinguishes all Liadytes from all Aspidytes Ribera, Beutel, Balke & Vogler, 2002 and is reported here for the first time. Since Liadytes and Aspidytes are the single genera in the respective families, we can use this character also for distinguishing between the Liadytidae and Aspidytidae. The monotypic genus Ovidytes and species O. gaoi Ren, Zhu & Lu, 1995 were described in the family Liadytidae (Ren et al. 1995). We could not study the type material of this species, but judging by the relatively short non-swimming legs, shown in an illustration to the original description, O. gaoi can hardly belong to Dytiscoidea., Published as part of Prokin, Alexander A., Petrov, Pyotr N., Wang, Bo & Ponomarenko, Alexander G., 2013, New fossil taxa and notes on the Mesozoic evolution of Liadytidae and Dytiscidae (Coleoptera), pp. 137-159 in Zootaxa 3666 (2) on page 140, DOI: 10.11646/zootaxa.3666.2.2, http://zenodo.org/record/220466

Palaeodytes baissiensis sp. n. Etymology: From Baisa (also known as Baissa, an alternative transliteration) fossil site; adjective in the nominative singular. Material: Holotype PIN 4210 / 380 ��, beetle without head, prothorax and larger part of legs; Baisa, Buryat Republic, Russia (Early Cretaceous, approximately Hauterivian, ca. 135 mya; Zherikhin et al. 1999). Description (Figs 16���18): Medium-sized beetle, with light underside and black elytron. Maximum body width situated at middle of metacoxae. Mesocoxae rounded, separated. Metacoxal plate 1.9 times as long as lateral lobe of metaventrite (LC/LV = 1.9). Metafemur dilated to 2 / 3 of its length, and then narrowed towards apex. Measurements: Body length, probably around 10 mm; body width, 4.8 mm (5.6 mm with the displaced elytron); elytron length, 8.3 mm. Comparison: The new species differs from P. gutta Ponomarenko, 1987 and P. sibiricus Ponomarenko, 1987 in its larger body size and black elytra; it also differs from P. sibiricus, described from the same locality, in the shape of the metafemur., Published as part of Prokin, Alexander A., Petrov, Pyotr N., Wang, Bo & Ponomarenko, Alexander G., 2013, New fossil taxa and notes on the Mesozoic evolution of Liadytidae and Dytiscidae (Coleoptera), pp. 137-159 in Zootaxa 3666 (2) on page 149, DOI: 10.11646/zootaxa.3666.2.2, http://zenodo.org/record/220466

Key to the genera of Mesozoic Dytiscidae (adults) 1. Metaventrite with straight posterior margins of lateral lobes, converging posteriad at obtuse angle (Fig. 23); elytra with dark stripes (subfamily incertae sedis).................................................................. Sinoporus. - Metaventrite with concave posterior margins of lateral lobes (e.g., as in Fig. 20); elytra without dark stripes............. 2. 2. LC/LV (ratio of maximum length of metacoxal plate and lateral lobe of metaventrite, both measured longitudinally, as in Fig. 22) around 1–1.7 (Liadytiscinae).......................................................................... 5 - LC/LV around 2 or greater (subfamily incertae sedis).......................................................... 3 3. Posterior and anterior margins of lateral lobe of metaventrite strongly converging, then slightly diverging again, then converging again near epipleuron; LC/LV around 3............................................. " Palaeodytes " incompletus. - Posterior and anterior margins of lateral lobe of metaventrite more or less evenly converging towards epipleuron......... 4. 4. LC/LV around 3 (as in Figs 19, 20)................................................................ Cretodytes. - LC/LV around 2.............................................................................. Palaeodytes. 5. Metacoxal lines weakly diverging anteriad; metacoxal processes with incision between them, conjointly truncate or rounded posteriorly, not narrowed anteriad (as in Figs 6, 7); LC/LV around 1; metatibia narrow and long, longer than metafemur (Liadytiscini)........................................................................................ 6. - Metacoxal lines strongly diverging anteriad; metacoxal processes slightly narrowed anteriad, with posterior margins rounded (as in Figs 8 –11, 12, 14); LC/LV around 1.2–1.7; metatibia subequal in length to or shorter than metafemur (Mesoderini trib. n.)................................................................................................. 8. 6. Metacoxal processes conjointly truncate posteriorly, with incision between them; metaventrite with laterally limited elevated median area triangular......................................................................... Liadytiscus. - Metacoxal processes conjointly truncate apically, with incision between them, or rounded with incision; metaventrite with elevated median area rounded or without such elevated area..................................................... 7. 7. Metacoxal processes more or less conjointly truncate posteriorly, with posterior margins appearing somewhat sinuate, with incision between them (as in Figs 6, 7)...................................................... Liadyxianus gen. n. - Metacoxal processes rounded.................................................................. Liadroporus. 8. Metaventrite with rounded laterally limited elevated median area (Figs 8–11)............................... Mesoderus. - Metaventrite without laterally limited elevated median area (Figs 12, 14)............................. Mesodytes gen. n.

Family Dytiscidae Leach, 1815, Published as part of Prokin, Alexander A., Petrov, Pyotr N., Wang, Bo & Ponomarenko, Alexander G., 2013, New fossil taxa and notes on the Mesozoic evolution of Liadytidae and Dytiscidae (Coleoptera), pp. 137-159 in Zootaxa 3666 (2) on page 141, DOI: 10.11646/zootaxa.3666.2.2, http://zenodo.org/record/220466

Mesoderus ovatus sp. n. Etymology: The Latin ovatus (egg-shaped); adjective in the nominative singular. Material: Holotype NIGP 154569, counter impression of beetle; China, Liutiaogou; Early Cretaceous, Yixian Formation. Description (Figs. 10, 11): Light coloured beetle. Maximum body width situated at middle of metacoxae. Pronotum 3.3 times as wide as long, 1.5 times as wide basally as at its anterior margin. Mesocoxae widely separated. Mesofemur with anterior margin straight and posterior margin convex, slightly protruding beyond body sides; mesotibia straight, with holes at bases of setae on ventral surface. Metacoxal plate 1.7 times as long as lateral lobe of metaventrite (LC/LV = 1.7). Metacoxal processes extended to level of abdominal ventrite 2. Metafemur and metatibia dilated towards their apices, metatibia slightly shorter than metafemur. First metatarsomere 1.8 times as long as metatarsomere 2 and equal in length to metatarsomeres 2 and 3 together; metatarsomeres 3 and 4 equal in length; metatarsomere 5 slightly shorter. Measurements: Body length, 10.8 mm; body width, 6.3 mm; elytron length, 8.7 mm. Comparison: Similar to M. ventralis Prokin & Ren, 2010 in size, but differs from it in the ratio of the length of the metacoxal plate and lateral lobe of the metaventrite, longer metacoxal processes, shape of meso- and metafemora and metatibia, and shorter metatarsomere 1., Published as part of Prokin, Alexander A., Petrov, Pyotr N., Wang, Bo & Ponomarenko, Alexander G., 2013, New fossil taxa and notes on the Mesozoic evolution of Liadytidae and Dytiscidae (Coleoptera), pp. 137-159 in Zootaxa 3666 (2) on page 147, DOI: 10.11646/zootaxa.3666.2.2, http://zenodo.org/record/220466

Cretodytes incertus sp. n. Etymology: From the Latin incertus (unclear); adjective in the nominative singular. Material: Holotype PIN 4626 / 628, direct impression of beetle without head, prothorax and legs; Chernovskiye Kopi (also transliterated as Chernovskie Kopi), Transbaikalia, Russia, left bank of the Ingoda River, Late Jurassic ��� Early Cretaceous, Doronino Formation. Description (Figs 19, 20): Small oval light beetle. Elytron thin, wing venation visible as loop at base of oblongum. Maximum body width situated at level of middle of metacoxal plates. Mesocoxae rounded. Metacoxal plate 3.3 times as long as lateral lobe of metaventrite (LC/LV = 3.3). Metacoxal processes rounded, slightly elevated above metacoxal plates. Measurements: Body length, probably around 7 mm; body width, 3.6 mm; elytron length, 5.3 mm. Comparison: The new species differs from C. latipes Ponomarenko, 1977 in the smaller body length and width and shorter lateral lobe of the metaventrite and metacoxal processes., Published as part of Prokin, Alexander A., Petrov, Pyotr N., Wang, Bo & Ponomarenko, Alexander G., 2013, New fossil taxa and notes on the Mesozoic evolution of Liadytidae and Dytiscidae (Coleoptera), pp. 137-159 in Zootaxa 3666 (2) on page 152, DOI: 10.11646/zootaxa.3666.2.2, http://zenodo.org/record/220466

Liadyxianus kirejtshuki sp. n. Etymology: In honour of the coleopterist A.G. Kirejtshuk; noun in the genitive case. Material: Holotype MNHN A 31864, counter impression of beetle; China, probably Huanbanjigou (label indicates only formation); Early Cretaceous, Yixian Formation. Description (Figs. 6, 7): Light coloured beetle. Head triangular, 1.5 times as wide as long. Pronotum 3.6 times as wide as long, with posterolateral angles rounded. Maximum body width situated at level of abdominal ventrite 1. Mesocoxae located close to each other. Mesofemur not dilated basally. Maximum length of metacoxal plate 0.9 times as great as maximum length of lateral lobe of metaventrite (LC/LV = 0.9). Metacoxal processes more or less conjointly truncate, with posterior margins appearing somewhat sinuate, reaching posterior margin of abdominal ventrite 1. Metafemur with sides slightly rounded. Metatibia slightly dilated towards its apex, slightly longer than metafemur; metatarsomere 1 somewhat shorter than metatarsomeres 2 and 3. Abdominal tergite 4 with round spiracle dorsally. Measurements: Body length, 7.4 mm; body width, 3.7 mm; elytron length, 5.9 mm.

Mesodytes rhantoides sp. n. Etymology: From the generic name Rhantus; adjective in the nominative singular. Material: Holotype NIGP 154570, counter impression of beetle; China, Liutiaogou; Early Cretaceous, Yixian Formation. Description (Figs. 12���15): Beetle with light underside. Head length 0.7 times as great as head width at level of posterior margins of eyes; obscured behind eyes, with two small dark spots in front of clypeus. Pronotum three times as wide as long, 1.4 times as wide basally as at its anterior margin; with rounded sides and angles, with basal angles slightly protruding posteriad; with broad dark stripe basally, broadly connected medially with narrow dark stripe running along entire anterior margin, narrowing and reaching or almost reaching anterior angles. Maximum body width situated at level of abdominal ventrite 2. Procoxae and mesocoxae closely set. Metacoxal plate approximately 1.2 times as long as lateral lobe of metaventrite (LC/LV ��� 1.2). Metafemur not dilated towards apex. Abdominal ventrites more or less equal in length; abdominal segments 3, 4, and 5 sublaterally with large oval spiracles. Penis evenly curved, with apex rounded and base dilated (see arrows in Fig. 15). Elytron translucent, with wing venation partly visible under elytron; with dark sutural and apical margin and at least 20 rows of dark spots. Elytral epipleuron translucent, without spots, wide; its internal margin forming sharp angle with lateral margin of elytron, starting at base of abdomen and ending at posterior edge of abdominal ventrite 4; maximum width situated at level of abdominal ventrite 2. Abdominal tergites 4, 5, and 6 with round spiracles dorsally. Measurements: Body length, 16.0 mm (17.7 mm including protruding genitalia); body width, 7.5 mm; elytron length, 10.1 mm., Published as part of Prokin, Alexander A., Petrov, Pyotr N., Wang, Bo & Ponomarenko, Alexander G., 2013, New fossil taxa and notes on the Mesozoic evolution of Liadytidae and Dytiscidae (Coleoptera), pp. 137-159 in Zootaxa 3666 (2) on pages 147-149, DOI: 10.11646/zootaxa.3666.2.2, http://zenodo.org/record/220466

Liadyxianus gen. n. Etymology: From the generic name Liadytiscus and Yixian Formation; gender masculine. Type species: Liadyxianus kirejtshuki sp. n. Diagnosis: Metacoxal plate somewhat shorter than lateral lobe of metaventrite (LC/LV slightly less than 1). Metaventrite with elevated rounded median area. Metacoxal lines weakly diverging anteriad. Metacoxal processes more or less conjointly truncate posteriorly, with posterior margins appearing somewhat sinuate, with incision between them. Lateral lobe of metaventrite not reaching lateral margin of metepisternum and metacoxal plate. Hindleg long, equal in length to abdomen. Metafemur, when stretched, reaching posterior margin of abdominal ventrite 3; metatibia longer than metafemur. Abdominal ventrite 1 shorter medially than any other abdominal ventrite; ventrite 2 longer medially than any other abdominal ventrite. Comparison: The new genus differs from Liadytiscus and Liadroporus in the shorter metafemur, when stretched, reaching posterior margin of ventrite 3, and metacoxa somewhat shorter than lobe of metaventrite. It differs from Liadroporus in the more or less conjointly truncate metacoxal processes., Published as part of Prokin, Alexander A., Petrov, Pyotr N., Wang, Bo & Ponomarenko, Alexander G., 2013, New fossil taxa and notes on the Mesozoic evolution of Liadytidae and Dytiscidae (Coleoptera), pp. 137-159 in Zootaxa 3666 (2) on page 143, DOI: 10.11646/zootaxa.3666.2.2, http://zenodo.org/record/220466

" Palaeodytes " incompletus Ponomarenko, Coram & Jarzembowski, 2005 This species was recently described from the Berriasian Purbek Limestone Group, UK. Its body outline is uncharacteristic of Palaeodytes (cf. fig. 4 in Ponomarenko et al. 2005: 280) and its lateral lobe of the metaventrite has a peculiar shape (resembling, e.g., that of the recent dytiscid Ilybius fenestratus (Fabricius, 1781), although it may be distantly related), with the posterior and anterior margins strongly converging and then slightly diverging again, and converging again near the epipleuron. The genus to which the species belongs is similar in morphological parameters to several recent genera of the family, and it is difficult to provide a diagnosis based on what is known about it. Having at present no opportunity to re-examine the holotype of this species in search of possible distinguishing characters of the genus, we refrain from describing the new genus here. Therefore, in this study the species is provisionally referred to hereinafter as " Palaeodytes " incompletus.

Cretodytes Ponomarenko, 1977 Type species: Cretodytes latipes Ponomarenko, 1977. Notes: The genus is characterized by the short lateral lobe of the metaventrite, deep and rather wide cavity at the apex of the anterior metaventral process, and elevated median platforms of metacoxae, which are weakly diverging, but dilated and rounded apically. It differs from Palaeodytes in the longest point of the metacoxal plate situated at the level of the external margin of mesocoxae, and in the shorter lateral lobe of the metaventrite (which also distinguishes it from Liadytiscinae); from " Palaeodytes " incompletus it differs in the shape of the lateral lobe of the metaventrite and shape of the metacoxal processes; and from Sinoporus, in the concave posterior margins of the lateral lobes of the metaventrite (cf. Figs 20 and 23). The new species belongs to this genus according to the combination of two characters: metacoxal plate three times as long as the lateral lobe of the metaventrite and absence of a laterally limited elevated median area of the metaventrite., Published as part of Prokin, Alexander A., Petrov, Pyotr N., Wang, Bo & Ponomarenko, Alexander G., 2013, New fossil taxa and notes on the Mesozoic evolution of Liadytidae and Dytiscidae (Coleoptera), pp. 137-159 in Zootaxa 3666 (2) on page 152, DOI: 10.11646/zootaxa.3666.2.2, http://zenodo.org/record/220466

Mesodytes gen. n. Etymology: From the Mesozoic and the Greek ��������ς (diver); gender masculine. Type species: Mesodytes rhantoides sp. n. Diagnosis: Elytron smooth, translucent, covered with matted rows of dark spots, separated by a distance greater than or equal to their diameter. Lobe of prosternal process flat, elongated, reaching mesocoxae. Maximum length of lateral lobe of metaventrite relatively great, but smaller than maximum length of metacoxal plate (LC/LV> 1). Lateral lobe of metaventrite not reaching lateral margins of metepisternum and mesocoxal plate. Metaventrite without elevated laterally limited area medially. Metacoxal lines weakly diverging anteriad. Metacoxal processes rounded posteriorly, slightly narrowed anteriad. Metafemur 1.5 times as long as metatibia. Metafemur, when outstretched, reaching middle of abdominal ventrite 4. First metatarsomere 1.5 times as long as metatarsomere 2. Comparison: The new genus differs from the genus Mesoderus in the absence of an elevated laterally limited area of the metaventrite, translucent and dark-spotted elytron, and shorter metatibia and metatarsomere 1., Published as part of Prokin, Alexander A., Petrov, Pyotr N., Wang, Bo & Ponomarenko, Alexander G., 2013, New fossil taxa and notes on the Mesozoic evolution of Liadytidae and Dytiscidae (Coleoptera), pp. 137-159 in Zootaxa 3666 (2) on page 147, DOI: 10.11646/zootaxa.3666.2.2, http://zenodo.org/record/220466

Liadytes aspidytoides sp. n. Etymology: From the generic name Aspidytes; adjective in the nominative singular. Material: Holotype PIN 2470 / 942 ��, beetle without head, prothorax and legs; Shar Teg, Upper Jurassic, beds 441, layer 4; paratype 2470 / 945, less complete impression of beetle from the same locality, beds 451 / 3; additional specimen (cannot be identified with certainty, therefore not included in the type series) PIN 2470 / 938, isolated elytron from the same locality, beds 451 / 3. Description (Figs. 1���5): Beetle with dark elytra, which appear black due to carbonisation of organic substance in oxygen-free environment, and pale body. Maximum body width situated at level of elytral base. Mesocoxae only slightly separated, rounded. Maximum length of metaxocal plate (measured parallel to longitudinal body axis) 1.2 times as great as maximum length of lateral lobe of metaventrite (measured in same manner) 3. Anterior margin of metacoxa weakly convex (metacoxal plate dilated anteriorly). Elevated median part of metacoxae with sides more or less straight, slightly diverging posteriad; metacoxal processes rounded posteriorly, with posterior margins meeting at an obtuse angle. Transverse suture of metaventrite present; median part of metacoxae elevated. Metepisternum 1.3 times as long as wide. Abdomen tapering from base of ventrite 4; ventrite 6 twice as long as ventrite 5. Elytron 3.4 times as long as wide. Epipleuron wide in its basal third, twice as wide as distally. Surface microsculpture of underside punctate, laterally on abdominal ventrites imbricate (according to Harris 1979). Measurements: Body length, probably around 7 mm; body width, 3.1���3.7 mm; elytron length, 4.6���5.3 mm. Comparison: The new species is similar to L. crassus Ponomarenko, 1977 in the convex anterior margins of the metacoxae (dilated anteriorly), but differs from it, as well as from the other species of Liadytes, in the presence of the elevated median part of the metacoxae (forming plates that partly cover the metafemora, as in Aspidytidae and Noteridae; these structures are, apparently, derived from the broader femoral plates of the metacoxae 4, homologous to those found in Haliplidae and many members of Geadephaga). Notes: The shape of femoral plates of the metacoxae and broad epipleuron of the new species are similar to those of Aspidytes, but the new species differs from it and from Noteridae in the mesocoxae located close to each other and in the absence of the anteromedial metaventral process (see above). The metacoxal plates dilated anteriorly are characteristic of Aspidytidae and Liadytiscinae (Dytiscidae) (see next section), but the new species differs from representatives of Liadytiscinae in the presence of the transverse suture on the metaventrite. Therefore, the new species is included here in the genus Liadytes (Liadytidae)., Published as part of Prokin, Alexander A., Petrov, Pyotr N., Wang, Bo & Ponomarenko, Alexander G., 2013, New fossil taxa and notes on the Mesozoic evolution of Liadytidae and Dytiscidae (Coleoptera), pp. 137-159 in Zootaxa 3666 (2) on page 141, DOI: 10.11646/zootaxa.3666.2.2, http://zenodo.org/record/220466

Mesoderus punctatus sp. n. Etymology: The Latin punctatus (spotted); adjective in the nominative singular. Material: Holotype NIGP 0 5622, counter impression of beetle; China, Liutiaogou; Early Cretaceous, Yixian Formation. Description (Figs. 8, 9): Light coloured beetle. Maximum body width situated at middle of abdominal ventrite 2. Elytron light, with dark spots, distance between spots twice as great as their diameter. Head length equal to width at posterior margin of eyes. Pronotum three times as wide as long, 1.6 times as wide basally as distally. Profemur narrowed towards apex; protarsal claws equal in length. Mesocoxae slightly separated. Mesofemur with anterior margin straight and posterior margin convex, slightly protruding beyond sides of body; mesotibia straight, with setose anterior margin. Metacoxal plate 1.2 times as long as lateral lobe of metaventrite (LC/LV = 1.2). Metafemur dilated towards apex. Metatibia straight, slightly shorter than metafemur, with swimming setae. Metatarsomere 1 with swimming setae, equal in length to metatarsomere 2; metatarsomere 2 equal in length to metatarsomeres 3 and 4 together; metatarsomere 5 short, only half as long as metatarsomere 4; claws of metatarsus equal in length, twice as long as metatarsomere 5. Penis pointed and curved (see arrow in Fig. 10). Measurements: Body length, 14.6 mm; body width, 7.5 mm; elytron length, 10.5 mm. Comparison: Similar to M. magnus Prokin & Ren, 2010 in size and in the pointed and curved penis, but differs from it in the dorsal coloration, LC/LV, longer metacoxal processes, shape of meso- and metafemora, and shorter metatarsomere 1., Published as part of Prokin, Alexander A., Petrov, Pyotr N., Wang, Bo & Ponomarenko, Alexander G., 2013, New fossil taxa and notes on the Mesozoic evolution of Liadytidae and Dytiscidae (Coleoptera), pp. 137-159 in Zootaxa 3666 (2) on pages 145-147, DOI: 10.11646/zootaxa.3666.2.2, http://zenodo.org/record/220466

Palaeodytes Ponomarenko, 1987 Type species: Palaeodytes sibiricus Ponomarenko, 1987. Notes: The genus is characterized by a short band-like pronotum and short head, together about 1 / 3 as long as the elytra; metacoxal plates longest in their lateral third (lateral of the external margins of the mesocoxae); lateral lobe of metaventrite half as long as metacoxal plate, median platforms of mesocoxae separated from the anterior margins of mesocoxae by a line, rounded apically and notched laterally; and dilated and flattened metatibia and metatarsus, the latter longer than the former. It differs from members of the subfamily Liadytiscinae in the shorter lateral lobe of the metaventrite, shorter and more dilated metatibia and metatarsus, and short pronotum; from Sinoporus it differs in the metaventrite with concave posterior margins of the lateral lobe (cf. Figs 17 and 23). The new species described below belongs to this genus according to the combination of two characters: metacoxa nearly twice as long as the lateral lobe of the metaventrite (LC/LV ��� 2), and absence of an elevated laterally limited area of the metaventrite., Published as part of Prokin, Alexander A., Petrov, Pyotr N., Wang, Bo & Ponomarenko, Alexander G., 2013, New fossil taxa and notes on the Mesozoic evolution of Liadytidae and Dytiscidae (Coleoptera), pp. 137-159 in Zootaxa 3666 (2) on page 149, DOI: 10.11646/zootaxa.3666.2.2, http://zenodo.org/record/220466