SuhjamUies, Genera, and Subgenera — Recent and Fossil 139 



is also a greater number of diverticula. The spermatheca is twice as long 

 (3 mm.) and the duct is longer (3.5 mm.). A cross section of the prostate 

 near the lower end shows seventeen rows of long, club-shaped diverticula 

 (fig. 12). In the penial complex (fig. 8), the preputium is normally very 

 wide, pyriform, with the vergic sac small and narrow and about half as 

 long as the preputium. In fig. 9, a penial complex is shown with the 

 preputium pushed upward. The immature penial complex (fig. 10) is very 

 wide with a short duct, as in other immature forms of Pierosoma. 



Helisoma corpulentum (Say) and its races inhabit the northern part of 

 the United States and southern Canada. The genitalia greatly resemble 

 those of H. pilsbri/i iniracarinatum. The principal features of the genitalia 

 are figured on plate 31. 



In corpulentum (fig. 3), the seminal vesicle (SV) is long and wide (4 

 mm. long, 0.7 mm. wide). The prostate is 5 mm. long, 1.5 mm. wide, and 

 1.5 mm. high (fig. 2). In cross section, this is seen to be composed of 

 twenty long diverticula arranged fan-wise. The ovotestis (OT) occupies 

 a trifle over one whorl and consists of about eighteen rows of long divertic- 

 ula (fig. 1). The spermatheca (S) is 2 mm. long and is placed at the end 

 of a very long duct (5 mm.). In form, the spermatheca is more nearly like 

 that of infracarinatum. The normal form of the penial complex is shown 

 in fig. 5, the preputium and vergic sac being about equal in length. Figure 4 

 shows a specimen in which the vergic sac is shortened and the upper part 

 of the preputium has been pushed upward, a common characteristic in 

 Pierosoma. The form of the penial complex in immature individuals is 

 shown in figs. 6 and 7, fig. 6 being from a younger specimen. 



A race of corpulentum, multicostatum F. C. Baker, has the genitalia 

 much as in the typical form. Figures 9 and 10 show the form of the penial 

 complex in immature individuals. Figure 11 is from an immature individual 

 in which the vergic sac has been lowered to the side of the preputium. 

 Figiu'e 12 also shows an immature condition. In fig. 13, the penial complex 

 of a fully mature individual is shown, the preputium pushed upward and 

 the long penial gland duct uncoiled (it is 14 mm. long). The penial gland 

 is shown in section in fig. 8. 



Another race found only in Lake Vermilion, Minnesota, H. c. vermilion- 

 ense F. C. Baker, shows no essential differences in its genitalia. The penial 

 gland is rather shallow (fig. 15) but this could be from contraction. Figure 

 14 shows one form of the penial complex when the j^reputium is pushed 

 upward. The gland duct is partly uncoiled. Figures 16, 17, and 18 show 

 the penial complex of immature individuals, progressively from 16 to 18. 

 The penial duct is short in figs. 16 and 17 but much longer in fig. 18, the 

 latter nearer maturitv. Two forms assumed bv the verge are shown in figs. 

 17 and 18. 



Helisoma ivhiteavesi F. C. Baker, a related species, apparently rare in 

 Canada, is similar in its genitalia to Helisoma corpulentum. The penial 

 complex of an adult individual is shown in fig. 19. The vergic sac differs 

 from that of the corpulentum group in being very long (5.5 mm.) and 

 slender. It is about as long as the preputium. The gland duct is very long 

 (24 mm.). Compare fig. 19 with fig. 13, the shells being of the same 

 size and age. 



A large Pierosoma, Helisoma magnificum. (Pilsbry) , living in Greenfield 

 pond, near Wilmington, North Carolina, resembles the northern pilsbryi 



