72 The Molluscau Family Planorhidae 



Subgenus TORQUIS Dall, 1905 

 Type by original designation Planorbis parvus Say 



1899. Gyrcudus (part) Martens, Biol. Cent. Amer., Moll., p. 392. Includes Planorbis 



parvus Say. 

 1905. Torquis Dall, Alaska Moll., pp. 83. 86. Type Planorbis parvus Say. As section 



of subgenus Gyraulus. 

 1918. Torquis W.\lker, Miscel. Contr., Mus. Zool., Univ. Mich., No. 6, pp. 34, 94. 



Type Planorbis parvus Say. As section of subgenus Gyraulus. 

 1921. Torquis Germain, Rec. Ind. Mus., XXI, pp. 8, 150. Type Planorbis parvus 



Say. As subgenus of Planorbis. 

 1923. Torquis Wenz, Fossil. Cat., Pars 22, p. 1627. Genotype Gyraulus (Torquis) 



Say. As subgenus of Gyraulus. 

 1926. Torquis Kennard and Woodw.\rd, British Xon-Marine Moll., p. 67. As section 



of Gyraulus in synonymy. 

 1926. Torquis F. C. Baker, Trans. Wis. Acad. Sci. and Arts. XXII, p. 204. Type Pla- 

 norbis parvus Say. As subgenus of Gyrajilus. 

 1928. Torquis F. C. Baker, Fresh-water Moll. Wis., I, p. 373. Type Planorbis parvus 



Say. As subgenus of Gyraulus. 



Shell (plate 77, figs. 4-6). Ultradextral, smaller than Gyraulus, SS, with 

 the whorls less distinctly spirally striated, not hirsute, the base (left side) 

 more or less concave, or excavated (appearing as though reamed out), the 

 lip often slightly thickened within. 



Animal. Not differing from Gyraulus in general form. 



ANATOMICAL CHARACTERISTICS 

 PLATE 17 (Gyraulus parvus) 



GENITALIA. Male Organs (fig. 6) . Seminal vesicle (SV) short (0.5 

 mm.) of the same diameter as the sperm duct. There are a number of small 

 glands which stand out like pustules. Sperm duct a trifle more than 1 mm. 

 in length. Prostate (PRS» more than half as long as the sperm duct with 

 eleven long and cylindrical diverticula. The free portion of the prostate 

 duct is very short (PD), joining with the sperm duct to form the vas 

 deferens. A cross section through the prostate shows the cylindrical or 

 pear-shaped diverticula on a separate duct which has a greater diameter 

 than the sperm duct (fig. 10). The vas deferens is at first a large duct 

 but becomes smaller in diameter toward the penial complex (VD). It is 

 about 1 mm. in length. 



The penial complex (fig. 6, VS, PR) is very long (about 1.3 mm.) and 

 narrow, and cylindrical. The vcrgic sac is longer than the preputium. There 

 is one large retractor muscle attached near the junction of the vergic sac 

 with the preputium (fig. 12, RIM). The vas deferens is not enlarged as it 

 enters the vergic sac. Internally (fig. 12) the preputium has two vertical 

 pilasters. The vergic sac is long and cylindrical and is enlarged at the 

 upper end (VS). The verge (V) is long and narrow, enlarged at the upper 

 end, very narrow below where there is a horny stylet (ST). The opening 

 of the sperm canal is on the side as in typical Gyraulus. Between the vergic 

 sac and the preputium there is a large papilla and below this a swelling 

 of the wall of the preputium representing the better-developed muscular 

 ring or diaphragm of typical Gyraulus (not shown in the figure). 



Female Organs. The spemiatheca (fig. 6, S) is small, pyriform, and 

 connected with the vagina by a duct about as long as the spermatheca 



