162 The Molluscan Family Planorbidae 



Shell (plate 78, figs. 20-22). Of medium size, ultradextral, globose, the 

 spire short and but little raised above the body whorl which is ventricose 

 and embraces most of the shell; aperture wide, greatly expanded; outer 

 lip thin, acute, somewhat reflexed in adult or old specimens; inner lip more 

 or less thickened; base convex or conical, imperforate or with but a small 

 chink. 



Animal (plate 36, fig. 1). Foot short, about half as broad as long. 

 Velum as in Helisoma. Tentacles short, cylindrical, blunt at the end, not 

 tapering. Eyes sessile at the inner base of the tentacles. The eyes are not 

 conspicuous in some preserved specimens. The body is darkly pigmented, 

 the pigmented areas extending to the head and sometimes forming streaks 

 on the tentacles. The posterior portion of the body is light gray. The ovo- 

 testis area is yellowish. 



ANATOMICAL CHARACTERISTICS 

 PLATE 36 {P(imi>hohjx cffuM, klamnthcnsis F. C. Baker) 



GENITALIA. Male Organs (fig. 3). Seminal vesicle (SV) about 4 

 mm. long, swollen, with many small vesicles projecting from the other- 

 wise smooth surface. The sju^rm duct (SPD) is about 3 mm. long and of 

 large diameter (0.4 mm. L The prostate (PRS) is long (3.5 mm.) and wide 

 and is composed of many small diverticula. In section (fig. 4), these di- 

 verticula are seen to be composed of about a dozen irregular follicles linked 

 together like sausages. From the outside of the prostate, these diverticula 

 appear to be covered with small tubercles irregularly placed. These follicles 

 enter the sperm duct at a common center, shown at X in the figure. The 

 vas deferens is about half the diameter of the sperm duct and is 11 mm. 

 long. 



The penial complex (fig. 7) is sac-like and is nearly 4 mm. in length. 

 The preputium is 1 mm. wide and occupies most of the length of the 

 penial complex. The vergic sac (VS) is 1 mm. long and 0.7 mm. wide. There 

 is only a slight constriction between the prejiutium and the vergic sac. 

 The penial gland duct is relatively short (about 1.5 mm. long) and rather 

 thick. It extends from the i)reputium near its upper third and enters the 

 vergic sac at the constricted area. The portion of the duct entering the 

 vergic sac and the preputium is very small and narrow, the duct swelling 

 greatly in diameter on the surface of the preputium. There are two sets 

 of retractor muscles, each set consisting of two main branches which sub- 

 divide several times at the penial sac insertions and at the connections 

 in the columella muscle. All insertions are on the preputium, none on the 

 vergic sac. There are several narrow supporting muscles (SAI) attached 

 to the preputium. 



Internally (fig. 9) , the preputium has two large, fleshy folds or pilasters 

 (PL). There is a mucii elongated, cylindrical penial gland (1.7 mm. long) 

 which resembles a pipe-stem, with a cup-shaped or bowl-shaped gland 

 (about 0.5 mm. in diameter) placed at the lower end (GL). The duct 

 (DC and X) enters the cylindrical portion of the gland and extends 

 through this stem-like portion, then enters the bowl-like cup of the gland 

 where it is enlarged into a bulb-like body (fig. 11, X). The cup-shaped 

 gland resembles the bowl of a pipe. In section (fig. 11), the cup shows a 

 shallow area at the top and the sides are lined with wide, thick folds (GF). 

 The bottom of the bowl-like cup is covered with small follicles which are 



