130 The Molluscan Family Planorbidae 



Shell (plate 80, figs. 7-12). Large, sinistral, physa-shaped or planorboid, 

 with every gradation between these forms, usually widely or deeply um- 

 bilicated; surface smooth, usually glossy, without the thread-like striae of 

 Pierosoma. 



Animal (plate 70, fig. 3 (adult), fig. 2 (young) ). With large velar area 

 and long tentacles as in Helisoma. Color variable. In scalare olivaceous, in 

 duryi and varieties dark olivaceous in old specimens, purplish on top of 

 head, fiecked with white. Bottom of foot dark horn or purplish, fiecked 

 with fine light dots. Tentacles lead color. Mantle yellowish or grayish over 

 lung and kidney, with few black or brown spots. Immature specimens are 

 more yellowish with few or no dots. The young animal is hyaline and 

 transparent, the internal organs yellowish or pinkish. 



ANATOMICAL CHARACTERISTICS 

 PLATE 28 



GENITALIA. Male Organs (fig. 14). Seminal vesicle (SV) about 2.5 

 mm. long, varying in width, but 1 mm. wide at the center and about 

 0.5 mm. wide anteriorly and posteriorly of this area. The seminal vesicle 

 is composed of many small glands. The ovisperm duct bears many 

 small vesicles along its side for over 1 mm. below the seminal vesicle. 

 Sperm duct nearly 3 mm. in length, of large diameter. Prostate (PRS) ob- 

 long, over 2 mm. in length composed of many diverticula arranged in fan- 

 like rows. A section of the prostate near the middle shows sixteen rows of 

 club-shaped diverticula (fig. 12). The prostate diverticula discharge into 

 a separate duct, the prostate duct, with which the sperm duct connects 

 posteriorly and the vas deferens anteriorly (see fig. 14). The vas deferens 

 (VD) is about 10 mm. long, and is about half the diameter of the sperm 

 duct. It is slightly enlarged (epiphallus) as it enters the vergic sac. 



The i^enial complex (fig. 10) is about 3.5 mm. long. The lower sac or 

 prei)utium (PR) is pyriform, 1.3 mm. wide at the upper part and less than 

 0.5 mm. wide at the male opening. There is one large retractor muscle 

 (RM) which is split into four branches at the preputium and in some 

 specimens (fig. 9) there may be one wide muscle of three branches with a 

 narrow, separate muscle below. The muscles are attached to the upper part 

 of the preputium. The supporting muscles (SM) usually form a wide band, 

 split into three branches at the upper part of the preputium. In one speci- 

 men there were five narrow, separate supporting muscles, each with two 

 branches, all placed near the lower end of the preputium (fig. 9). 



The duct of the penial gland (DC) is rather short (3.5 mm. long) and 

 tapers in diameter toward the end entering the vergic sac (fig. 6). The 

 vergic sac is of about the same length as the preputium, ovate-pyriform 

 in shape, about 1 mm. wide near the upper part of the sac. In some speci- 

 mens examined (fig. 9) , the preputium was pushed upward and the vergic 

 sac appeared as though attached to the lower part of the preputium. In 

 this condition, the penial gland duct extends from the top of the preputium 

 and enters the vergic sac below the level of the duct's exit. This condition 

 is observed in specimens in breeding stage. 



Internally (fig. 11), the preputial sac contains several (four or more) 

 narrow, slight, vertical ridges or pilasters (PL). The cavity of the pre- 

 putium is partly filled by an elongate-ovate (irregularly paralleliform) 

 penial gland attached by a short neck of less diameter to the body wall 



