320 PROCEEDINGS OF THE NATIONAL MUSEUM vol. iw 



Spermiducal gland larger than bursa, entally divided into two large, 

 subequal deferent lobes, the posterior lobe directed caudoventrad 

 and concealing ectal half of the ejaculatory duct and apex of penial 

 sheath. Prostate quite slender and short, its histology similar to that 

 of spermiducal gland, no terminal bulb detected. 



Spermatheca tripartite, consisting of a slender muscular ectal duct, 

 a somewhat translucent, globosely enlarged median sperm reservoir, 

 and an abruptly set-off glandular ental process. 



Variation.^ — All of the specimens examined are essentially similar 

 in structural features, varying chiefly in size. The bulbar portion of 

 the spermatheca varies considerably in its relative size and globosity, 

 from merely fusiform to nearly sphaeroid appearance. 



Affinities. — Of the known species of the genus, shoshone appears to 

 be structurally most like branchiophila. That the relationship is due 

 to convergence cannot, however, be discounted. Here the matter 

 must rest until additional species have come to light. 



Distribution. — Known only from the type locality, a tributary 

 of the Snake River in the southwestern part of Idaho, 



PHILADELPHICA SECTION 



The species comprehended in tliis major subdivision of the genus 

 include the most widespread and frec^uently encountered forms. 

 Most of them are already known from a considerable number of 

 localities, although a few appear to be localized. Resolution of 

 specific identities in this section has proved to be the major problem 

 in the revision, as the species in the Philadelphica group are generally 

 similar and difficult to separate. 



This section is characterized by the form of the male reproductive 

 system. The prostate is histologically quite different from the sper- 

 miducal gland, being composed of large cuboidal cells containing little 

 or no granular material and apparently with no well-defined nuclei. 

 Entally, the prostate terminates in a clear bulbous development, the 

 function of which is still unknown. Possibly it is related to some 

 hydrostatic function of the prostate, as the relative size varies slightly 

 in different individuals. 



Within the limits set by the preceding definition, there is consider- 

 able variation in body form, size, jaw structure, and details of the sex 

 organs. The range of variability in each category is as great as ob- 

 served for the entire genus, reflecting perhaps considerable evolu- 

 tionary radiation subsequent to the differentiation and specialization 

 of the prostate, but in general the overall facies of all the species is 

 basically similar and leaves little doubt about the homogeneity of the 

 section. 



