Subfamilies, Genera, and Subgenera — Recent and Fossil 73 



fSD). The vagina is narrow and about as long as tlie spernuitheca and 

 its duct. The uterus and nidamental gland are relatively short and wide 

 (U). The oviduct is short (about 0.5 mm.). The junction of the oviduct 

 and sperm duct to form the ovisperm duct is shown in fig. 7. The albumen 

 gland is squarish in form, longer than wide (about 1 mm. long), and is 

 composed of large diverticula. Its duct is long and looped (fig. 9, DA). 



Hermaphrodite Organs. The ovotestis is rather short and is composed 

 of Init few club-sha})e(l diverticula arranged in a double row (fig. 6, OT; 

 fig. 11). The ovisperm duct is small and tube-like and is longer between 

 the seminal vesicle and the ovotestis than between the seminal vesicle and 

 the oviduct (fig. 6, SO). Several of the diverticula of the ovotestis were 

 filled with ova ready for extrusion (fig. 11). 



Several other species of the subgenus Torquis have been dissected and 

 may be compared with parvus. Gyraidus circumstriatus (Tryon) (i)late 17, 

 fig. 1, also fig. 4) is similar in form. The prostate has twelve diverticula. 

 The spcrmatheca is the same. The duct to the albumen gland is not so long 

 ( fig. 2) . The penial complex is the same in both species which are of about 

 the same size. In Gyraulus vermicularis (Gould) there are sixteen diver- 

 ticula in the prostate and ten diverticula in the ovotestis (plate 15, fig. 10). 

 The penial complex is somewhat different, the preputium being long and 

 cylindrical and the vergic sac very short, only about half as long as the 

 preputium. In Gyraidus similaris (F. C. Baker) (plate 18, fig. 1) there are 

 nineteen diverticula on the prostate and the ovotestis diverticula are few 

 in number. In the penial complex the vergic sac is shorter than the 

 preputium. There is a heavy swelling at the upper part of the preputium 

 where the papilla and muscular ring are located. A section through the 

 penial complex (fig. 3) shows the relationship between the several organs. 

 The verge is very long and slender and has a large stylet (fig. 4). The 

 junction of oviduct, sperm duct, and ovisperm duct is shown in fig. 2. 



The genitalia of the subgenus Torquis differ from those of typical 

 Gyraidus in the form of the seminal vesicle, the fewer diverticula of the 

 prostate, and the rounder spermatheca on a shorter duct. In general, how- 

 ever, the two groups are very similar in the form and position of the 

 genital organs. No figures of the genitalia of the Torquis group have been 

 iniblished jireviously; hence no comparisons can be made. 



Respiratory and Renal Systems. The jiseudobranch of Gyraidus parvus 

 (plate 17, fig. 8) is flattened, wide, leaf-like, and is pierced by the rectum. 

 The pneumostome is very large. In Gyraulus circumstriatus (fig. 3) the 

 pseuclobranch is much narrower (the animal was much contracted). In 

 Gyraidus vermicularis (plate 15, fig. 8) it is flattened and somewhat tri- 

 angular. In Gyraulus similaris (plate 18, fig. 5) it is like that of vermicu- 

 laris but the rectum has a slight ridge which was not observed in any of the 

 other species examined. In the four species of this group studied there was 

 a large, flattened, muscular jiad extending backward from the free portion 

 of the pseudobranch to the place where the rectum begins on the intestine. 

 Figure 5 on plate 18 and fig. 8 on plate 15 show the form of this pad. The 

 rectum pierces this pad as well as the pseudobranch and has its exit (A) 

 above the leaf-like pseudobranch. 



The kidney (plate 47, fig. 1, parvus) is very long and narrow (4 mm. 

 long, 0.5 mm. wide), the ureter short and recurved. In Gyraidus circum- 



