140 The Molluscau Family Planorbidae 



and corpulentum. The prostate is 7 mm. long and more than 1 mm. wide 

 and high. There are thirteen rows of diverticula. The spermathecal duct is 

 very long (12 mm.) and narrow, and the spermatheca is 3 mm. long. The 

 organs of the female system are long and narrow. The penial complex 

 (fig. 20) has a pyriform preputium and a cylindrical vergic sac. The penial 

 gland duct is very long. Internally, the complex shows a large gland and a 

 cylindrical verge, both nearly filling their respective cavities (fig. 21). A 

 cross section of the penial gland is shown in fig. 22. It is much like that of 

 trivolvis. 



Species of the Rocky IMountains and Westward 



Several species and races of Pierosoma occur in the western part of the 

 United States and Canada. One of the most abundant and widely dis- 

 tributed species is Helisoma subcrenatuni (Carpenter), the genitalia of 

 which are figured on plate 30 (specimen not quite mature). Figure 15 

 pictures the whole genitalia, the organs spread out. The seminal vesicle is 

 2 mm. long and is notable for the number of rather long vesicles, princi- 

 pally bordering the gland, which is much wider than the ovisperm duct. 

 The sperm duct (SPD) is short (2 mm. long) and the vas deferens is 

 narrow and about 7 mm. long. The prostate is about 2 mm. long and is 

 composed of twenty- four rows of diverticula, arranged fan-wise when seen 

 in section (fig. 12). There is a short prostate duct at each end of the 

 prostate which joins the sperm duct beneath the prostate. The spermatheca 

 (S) is about 1 mm. long and the duct is long and narrow and about 2 mm. 

 long. The uterus (U) is narrow anteriorly and widens posteriorly into the 

 nidamental gland (NG), which is a large organ 1 mm. wide. The oviduct 

 (OD) is a narrow tube about 2 mm. long. 



The penial complex is about 3.5 mm. long in fully adult specimens (figs. 

 17, 19). The vergic sac is slightly shorter than the jireputium. The pre- 

 putium is widely pyriform while the vergic sac is narrow and cylindrical. 

 The penial gland duct is not very long (3 to 4 mm.) and is normally coiled 

 on the preputium. In vertical section (fig. 13), the penial complex shows 

 a large penial gland (GL), a rather thick diaphragm (D), and a thick, 

 somewhat sausage-shaped verge (V). In section, the penial gland (fig. 11) 

 is similar to that organ in trivolvis. In immature individuals, the penial 

 complex is very wide and the duct is very short (fig. 10). In fig. 15, the 

 penial duct and complex is of a young specimen. In adult or old specimens, 

 there is more difference between the preputium and vergic sac and the duct 

 is always longer. These differences are shown in figs. 17 and 18 (compare 

 with figs. 10 and 15). 



The genitalia of subcrenatum differ from those of the trivolvis group 

 in the greater number of prostate diverticula, shorter penial gland duct, 

 when adult, and the presence of the aculeate vesicles in the seminal vesicle. 



A relative of subcrenatum, H. plexatmn (Ingersoll), is figured on plate 

 30, fig. 4 (genitalia). The general characteristics of plexatum are like 

 subcrenatum. The seminal vesicle (SV), however, is different in the absence 

 of the digitate vesicles and is more like the seminal vesicle in pilsbryi. The 

 prostate is 5 mm. long and more than 1 mm. wide. The spermatheca (S) 

 is very narrow, over 2 mm. long, and the duct is 5 mm. long or nearly 

 three times the length of the spermatheca. It resembles the spermatheca 

 of trivolvis. The vergic sac is small and less than half the length of the 



