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Cacoxenus Loew is redefined on the basis of the type species, C. indagator , which is redescribed (including characteristics of the genitalia) and for which a lectotype is selected. Paracacoxenus Hardy, type P. guttatus Hardy and Wheeler (Washington and Oregon), is allied to Cacoxenus, Gitona , and Gitonides .

Imagoes of Drosophila endobranchia, n. sp., were collected from the carapace and legs of 2 species of land crabs, Gecarcinus ruricola (L.) and G. lateralis Freminville, in the Cayman Islands, West Indies. Studies of the anatomy and especially the male genitalia, which have some curious asymmetrical features, indicate that the species is a primitive member of the subgenus Drosophila, showing resemblances to the quinaria Loew and virilis Sturtevant species-groups. Thus, it is only moderately closely related to D. carcinophila Wheeler of the repleta Wollaston species-group. D. carcinophila, which is also subgenus Drosophila, is an associate of G. ruricola in the Greater and Lesser Antilles and the Bahamas. It has not been found in the Cayman Islands. D. endobranchia oviposits around the eyes of the crab; firstinstar larvae move beneath the third maxillipeds and thence into the gill chambers. Following a lengthy sojourn there, they move to the peribuccal region and then drop off and pupate in soil or sand.

Cuando se hacen las necesarias concesiones a la taxonomía corriente de las Drosophilidae, se ve que 15 especies, de las cuales 11 son Drosophila y 4 no Drosophila Drosophilidae, se han informado previamente de Puerto Rico. Recientemente, aunque no en forma extensiva, el esfuerzo hecho por colector este género de insectos en la Isla ha redundado en la captura de 27 especies de Drosophilidae. Ocho especies no Drosophila Drosophilidae y 15 especies Drosophila incluidas en las recientes colecciones no se habían informado previamente de Puerto Rico. Entre estas formas sin informar hay 2 nuevas especies de Drosophila las cuales se informan en este trabajo. El número de especies de Drosophilidae, hasta ahora informado de Puerto Rico, compara favorablemente con el de la peninsula de Florida, al sur del paralelo 29.

Sternites of the dipterous abdomen, as seen in cleared preparations at about 430x magnification, typically possess a pair of minute sensilla trichodea along the basal border. By using these as markers of modified or “lost” sternites, it was determined that males (as well as females) of the Drosophilidae possess seven sternites in the preabdomen, and that reduction has occurred in varying degrees among the species examined. Reduction, leading toward ultimate loss, includes loss of macrochaetae, loss of sclerotization, and loss of sensilla; some sternites have become separated into two pieces in this process. Various types of vestigial sternites still present indicate that the sequence of steps leading toward sternite disappearance is not constant. Suggestions are made as to the steps which might have been involved in sternite modification leading to incorporation as genitalial pieces.

General descriptions, including detailed figures of the male genitalia and wing photographs, are presented for the two described American species of Mycodrosophila, dimidiata (Loew) and projectans (Sturtevant), and for two new Nearctic and five new Neotropical species of this genus. New species are: claytonae (Florida to Ontario, west to Montana, Colorado, and Texas); stalked (Florida to Ontario, west to Texas); elegans (Panama to Brazil); brunnescens (Brazil); pseudoprojectans (Nicaragua to Colombia); neoprojectans (Honduras to Ecuador); and nigropleura (Greater Antilles, El Salvador, and Honduras).

There is mounting evidence that Drosophila populations are mlore polymorphic at the level of genetic loci than was formerly thought by many geneticists. There have been many experimental demonstrations of the extensive chromosomal polymorphis^ms, of the presence of considerable quantities of hidden deleterious and lethal alleles in the populations, and of the extensive complexity of the coadapted genetic systems integrated through natural selection.' Nevertheless, the proportion of polymorphisms among the majority of all loci is largely unknown because of inadequate screening techniques. Furthermore, the mechanisms for the maintenance of polymorphisms -remain elusive to experimental verification. The ideal situation of screening populations for genetic comparisons at and between individual loci has been brought a step closer to reality by electrophoretic separation of enzyme molecules. Though enzyme differences are not necessarily related with genetic differences on a one-to-one basis, most may be. At any rate, zymogram analysis of individual flies for electrophoretic mobility or qualitative activity differences gives a good first approximation of the underlying genetic situation for a different class of variation than has previously been studied directly. However, as Lewontin and Hubby3 have pointed out, the randomness of the samples of loci studied by this technique is critical for broader generalizations which might be made from the findings in this class of loci. Sample characteristics are yet to be determined. Lewontin and Hubby3 have found about 40 per cent of all electrophoretically separable enzyme systems and protein bands of no known enzymatic activity of D. pseudoobscura to be polymorphic, having two or more electrophoretic forms of the same protein. One expects the difference in molecular forms to represent at least as much genetic difference, so that the variation of molecular types reflects similar variation of genotypes. If only a moderate bias is involved in estimating this proportion for the genome, then there exists a major discrepancy between the data and the expectation based upon the theory of segregational load. According to the theory, a population may bear, without being jeopardized by reduced average fitness, only a relatively small portion of loci in heterotic polymorphic conditions. In order to establish the meaning of the apparent inconsistency between the theory and observations, it must be established whether or not these isozyme polymorphisms are maintained more or less independently by some form of selection. It is very important to know if these variations are random representatives of a large number of such loci. It has been demonstrated in a laboratory population of D. busckii4 that the polymorphism at the "leucine aminopeptidase" locus is maintained by heterotic selection, though this was not the case for an esterase locus in D. inelanogaster and D. simulans.5

We have found five distinct chromosomal regions which are repeated within the genomes of 11 endemic Hawaiian Drosophila species. One of the duplications was observed in more than 130 species (of three genera) of Hawaiian Drosophilidae. These "repeats" show synapsis in some nuclei, not in others; repeated segments are sometimes tandem while others are separated on their respective chromosomes. From these observations, one can speculate that chromosomal rearrangements produced by unequal crossing over due to such "repeats," and the possible development of new or modified gene action may provide, at least in part, an explanation of the remarkably rapid evolution and speciation in Hawaiian Drosophila.

Drosophila immigrans Sturtevant was reported from the Galapagos by Curran (1934), and as far as I have been able to determine this is the only species of the Drosophilidae recorded from these little-known islands. Among some Drosophilidae sent to me by workers at the U. S. National Museum for identification were 45 specimens from the Galapagos, representing four species, collected by K. Vinton during July and August 1948. Drosophila immigrans was not among them. The four additional species records are as follows

The widespread American species called "transversa" is shown to be undescribed, while the Rocky Mountain species, subquinaria Spencer, agrees in most respects with the European transversa. Three new species of this complex are described: Drosophila falleni from Ontario to Florida to Texas to Minnesota; recens from North Dakota to Maine and Ontario; and rellima from Nebraska, Oregon and California. The European species Drosophila transversa Fallen was first re- ported from North America by Loew (1864), and later authors have continued to use this name for a common species of the eastern United States. Hsu (1949) pointed out, however, that the male genitalia of American specimens differed from that of "transversa" from Switzer- land and from China. In reinvestigating this problem I have had the loan of additional material from the U. S. National Museum, through the assistance of Dr. W. W. Wirth, and from the Canadian National Collection, through the assistance of Dr. J. F. McAlpine. In addition, Mr. E. B. Basden of Edinburgh, Scotland, has most generously supplied speci- mens, drawings, photographs and copious notes on true European transversa, including data on the lectotype and syntypes from Falldn's collection. It is now clear that the widespread American species going under the name transversa is quite distinct; it is described below as Dro- sophila falleni in honor of the famous dipterist who established the genus Drosophila in 1823. Examination of the male genitalia of some American members of the quinaria species group revealed, however, that Drosophila sub- quinaria Spencer is extremely similar to the true transversa; hybridi- zation tests between them will be carried out in the near future to confirm or deny this possible synonymy. During this study two additional new species of the quinaria group were discovered; these are described below as D. recens and rellima. Holotypes of the new species are in the Drosophila Type and Refer- ence Collection of the University of Texas, Austin. Some paratypes

Four new species of acalyptrate flies are described, as follows: Family Ephydridae-Scatophila iowana from Iowa; Notiphila (Agrolimna) hamif- era from Arizona and Colorado; Family Chyromyiidae-Aphaniosoma frontata from California, Arizona, Utah and Baja California (Mexico); Aphaniosoma aldrichi from Texas. The holotype and allotype specimens of the new species described below are being placed in the U.S. National Museum collection. The disposition of the paratypes is indicated separately for each species.

Three new species of the dipterous family Drosophilidae are de- scribed: Chymomyza olympia from Washington, formerly reported as "?distincta Egger"; Leucophenga neovaria from Florida, Puerto Rico, Jamaica, El Salvador, Nicaragua, Colombia and Venezuela; and Amiota huachucae from Arizona, formerly reported as albavictoria Patterson and Mainland. Two of the new species described here have been previously re- ported from the United States, but as tentative or erroneous identifica- tions of named species. The Holotypes are in the Drosophila Type and Reference Collection of the University of Texas. Some paratypes of each species are being placed in the U.S. National Museum collection.