no. 3602 CRAYFISHES — HOBBS, HOLT, AND WALTON 15 



passed to them by the second antenna. The terminal claws of the 

 latter collect the particles entrapped by the setae of the host. Fecal 

 pellets contain mostly a finely divided brown material (the origin of 

 which is not known) , small translucent refractive fragments, portions 

 of diatoms, small rods (presumably bacilli), and what are believed 

 to be spore cases. Furthermore we have not observed a single 

 ostracod among the gill filaments, where, were they parasitic, they 

 would most likely occur. 



The branchiobdellids. — There is a persistent tradition that 

 branchiobdellids are parasitic; this is certainly not true of most 

 species, but almost surely it is true of the gill-inhabiting forms. Small- 

 wood (1906, p. 100) found the gut of Xironogiton instabilius always 

 full of algae and thought he found the same for Bdellodrilus illuminatus. 

 Since the latter is confined to gill chambers, Smallwood probably was 

 dealing instead with a species of Cambarincola that is not gill-inhabit- 

 ing. Hall (1914, p. 189), on the basis of pieces of striated muscle 

 fibers found in the lumen of the intestine, reported that adults of 

 Ceratodrilus thysanosomus are parasitic. These fibers, however, prob- 

 ably were derived from ingested insect larvae rather than from the 

 hosts. Goodnight (1940, p. 66) reviewed these and other similar 

 comments and added his opinion that diatoms are the "favorite" 

 food of most species. The truth is that no careful studies of the food 

 and feeding habits have been made. It can, nevertheless, be said of 

 the species encountered in the present study that Bdellodrilus illumi- 

 natus is parasitic, feeding on the gill filaments of the host; probably 

 the same is true of Cambarincola branchiophila. Pterodrilus alcicornus 

 is particularly partial to diatoms, which constitute the vast bulk of 

 the food of this species. The larger species of Cambarincola show 

 carnivorous and cannibalistic tendencies as well. Whether or not the 

 other species of the area have a specialized diet cannot be said, for 

 all branchiobdellids, except the gill-inhabiting parasites, appear to 

 feed simply by grazing on the unicellular algae, bacterial gloea, and 

 the animals, except the ostracods, that make up the flora and fauna 

 that are borne by crayfishes. 



The Crayfishes 



The key that is provided for the identification of the crayfishes of 

 the region can be used reliably only in the immediate area. In order 

 to facilitate the rapid identification of specimens of both sexes, the 

 secondary sexual characters that are definitive for generic determi- 

 nations, and some specific ones as well, have been disregarded. 



The male crayfishes of the area, like all members of the subfamilies 

 of the Astacidae except the Astacinae, exhibit a cyclic dimorphism 



