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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.

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).

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