Suhfamilies, Genera, and Subgenera — Recent and Fossil 135 



1905. Pierosoma Dall, Alaska Moll., pp. 81, 85. Type Planorbis trivolvis Say. As 



section under subgenus Helisoma 

 1918. P/emso ma Walker, Miscel. Pub. Mus. Zool., Univ. Mich., No. 6, p. 11. Type 



Planorbis trivolvis Say. As section of subgenus Helisoma 

 1921. Pierosoma Germain, Rec. Ind. Mus., XXI, pp. 6, 49. Type Planorbis trivolvis 



Say. As subgenus 

 1923. Pierosoma Wenz, Fossil. Cat., Pars 22, p. 1522. Genotype H. (Pierosoma) trivol- 

 vis (Say.) As svibgenus. 

 1926. Pierosoma F. C. Baker, Trans. Wis. Acad. Arts and Science, XXII, p. 202. Type 



Planorbis trivolvis Say. As subgenus 

 1928. Pierosoma F. C. Baker, Fresh-water Moll. Wis., I, p. 329. Type Planorbis 



trivolvis Say. Genitalia and radula. As subgenus 

 1931. Pierosoma F. C. Baker, Proc. Zool. Soc. London, p. 586. Tjq^e Planorbis trivolvis 



Say. Genitalia and radula. As subgenus 

 1931. Pierosoma Thiele, Handbuch, Teil 2, p. 479. Type Planorbis trivolvis Say. 



As section of Planorbis 

 1934. Pierosoma Pilsbry, Proc. Acad. Nat. Sci. Phil., 86, p. 30. As subgenus 



Shell (plate 80, figs. 13-15) . Large, sinistral, of few whorls, the last whorl 

 large and capacious, the early whorls usually flattened and carinate above, 

 widelj^ umbilicate below ; spire of the adult shell usually flattened and sunk 

 below the level of the body whorl ; aperture notably expanding, even flar- 

 ing in some specimens, the outer lip thickened within; sculpture of coarse 

 growth lines and conspicuous spiral lines; surface usually dull, never glossy 

 as in Seminolina. 



Animal (plate 70, fig. 7, H. trivolvis macrostomum; fig. 8, H. trivolvis 

 Jallax). Body long and somewhat narrow, rounded before, the foot nar- 

 rowly pointed behind; velar area well-developed; tentacles long and fili- 

 form; eyes at base of tentacles as in other Planorbidae. Color usually 

 dark horn, in some species reddish or yellowish, the body flecked with 

 streaks or spots; mantle spotted, as in trivolvis, or without spots, as in 

 pilsbryi; the head and foot are usually lead color. In the young, the ten- 

 tacles are very long and slender, the body dark horn color flecked wath 

 white spots; the eyes black; viscera reddish through the shell; foot also 

 somewhat reddish, especially on the front portion (plate 70, fig. 6) . 



ANATOMICAL CHARACTERISTICS 

 PLATE 24 (Planorbis trivolvis Say) 



GENITALIA. Male Organs (fig. 15) . Seminal vesicle (SV) elongated 

 (3.5 mm. long, 0.5 mm. wide) composed of many small vesicles. It occupies 

 almost half of the length of the ovisperm duct. Sperm duct (SPD) long and 

 narrow (about 4 mm. long) . Prostate (PRS) about 4.5 mm. long and 1 mm. 

 wide, composed of fourteen rows of diverticula emptying into a short 

 prostate duct which connects with the sperm duct and from which the long 

 (15 mm.) vas deferens (VD) extends and passes to the vergic sac. There is 

 only a very slight enlargement (epiphallus) of the vas deferens as it enters 

 the vergic sac. A cross section of the prostate (fig. 13) shows the fourteen 

 rows of diverticula to be of unequal length and the whole section to be 

 fan-shaped. 



The penial complex (fig. 11) is usually about 5 mm. long. The prepu- 

 tium (PR) is very wide (1.5 mm.) and cylindrical in shape. The vergic 

 sac (VS) is of the same length as the preputium but is very narrow, the 

 preputium rapidly narrowing as it receives the vergic sac. The vergic sac 



