Subfamilies, Genera, and Subgenera — Recent and Fossil 141 



preputium (fig. 1). In vertical section, the penial complex shows the penial 

 gland to be compressed as in subcrenatum (fig. 3) and not globular as in 

 trivoivis. The penial gland duct is longer than in subcrenatum (figs. 1, 2, 3) , 

 resembling trivoivis in this respect (compare figs. 1 and 17). The penial 

 gland is shown in section in fig. 5. The verge (V) is large and long ovate 

 in form when at rest (fig. 6). The shapes assumed during extension into the 

 vergic sac cavity are shown in figs. 7, 8, and 9. The retractor muscles are 

 as in subcrenatum. 



The penial complex of a form of subcrenatum from Pass Lake, Fidalgo 

 Island, Puget Sound, Washington, is figured on plate 32 (fig. 8). It is 

 similar in form to the penial complex of subcrenatum figured on plate 30 

 (fig. 17), the preputium, however, being more cylindrical and less pear- 

 shaped and the vergic sac is relatively longer. The presence of the two 

 small and narrow retractor muscles is noteworthy. 



Another form related to subcrenatum, but believed to be of specific rank, 

 is Helisoma horni (Tryon) from Paul Lake, British Columbia. The geni- 

 talia are different from both subcrenatum and ple.ratum (plate 26, fig. 3). 

 The seminal vesicle is similar to that of plexatum. The prostate is about 

 3 mm. long, and 1 mm. wide and has thirteen rows of large, club-shaped 

 diverticula (fig. 5). These are much wider and less in number than in 

 subcrenatum. The spermatheca (S) is bulbous, about 1 mm. in length and 

 the duct is 3 mm. long, widening as it enters the narrow vagina. The 

 ]icnial complex (fig. 1) has a long vergic sac enlarged at the outer end. 

 The preputium is pushed upward. The gland duct is about as long as in 

 plexatum. The penial gland (fig. 2) is like that organ in trivoivis. A sec- 

 tion through the sperm duct, oviduct and nidamental gland (fig. 4) indi- 

 cates the relationship between these organs. 



IMany years ago Tryon described a small Planorbis from Pueblo Valley, 

 Oregon, calling it Planorbis oregonensis (now Helisoma oregonense) . This 

 species has been one of the rarities of western Planorbidae. Specimens 

 collected in Tooele County, Utah, by Mr. J. Henderson belong to this 

 species and the anatomy of this small planorbid is now available. On plate 

 28, fig. 2, the principal organs of the genitalia are shown. 



The seminal vesicle is about 1 mm. long and the ovisperm duct about 

 3 mm. long. The latter bears short lateral vesicles for a large part of its 

 length, as in ple.vatum. The prostate is short (about 2 mm. long) and bears 

 sixteen rows of long and narrow diverticula (fig. 3). The spermatheca is 

 bulbous, about 0.7 mm. in length and connects with the long and narrow 

 vagina by a duct slightly more than 1 mm. in length. The shape of the 

 spermatheca is like that of horni but the duct is shorter. The penial com- 

 plex (fig. 1) has a large, pyriform preputium with the lower part length- 

 ened. The vergic sac is short, swollen at the end, and almost half the length 

 of the preputium. The penial gland duct is very long (5 mm.). There is 

 one retractor muscle (sometimes split into two smaller muscles), attached 

 to the lower part of the preputium, and one band of supporting muscle. The 

 ]ienial gland (fig. 4) is round, rather short, and attached to the wall of the 

 preputium by a short, wide neck. In vertical section (fig. 5), the cup is 

 circular, with relatively few large vertical folds and a number of pave- 

 ment-like folds in the bottom of the cup, to which the gland duct is 

 connected (DC). 



