52 The Molluscan Family Planorbidae 



1929. Planorbis (of Miiller 1774) Haas, Trab. Mus. Cien. Nat. Barcelona, XIII, p. 379. 



Tj'pe evidently intended to be Planorbis phniorbis (Linn.). As genus. 



1930. Planorbis H. B. Baker, Oc. Papers, Mus. Zool. Univ. Mich., No. 210, p. 42. Type 



b.y absolute tautonomy Helix planorbis Linn. As genus. 



1931. Planorbis Germain, Moll. Terr, et Fluv. France, II, pp. 516, 521. No type desig- 



nation. As genus and subgenus. 

 1931. Tropidiscm Thiele, Handbuch, IV, Teil 2. p. 481. Type Plaiiorbis planorbis 

 (Linn.). As subgenus. 



1935. Tropidiscus Soos, Allat. Kozlem., XXXII, p. 29. Planorbis carinatus Miiller and 



Planorbis planorbis (Linn.) cited. As subgenus under genus Anisus. 



1936. Planorbis (of Miiller 1774) R\as, Abh. Senckn. Natur. Gesell., No. 431, p. 25. 



Planorbis planorbis (Linn.) by absolute tautonomy. As genus. 



Shell (plate 77, figs. 26-28) discoidal with few whorls, regularly in- 

 creasing in diameter; upper and lower (left and right) sides flattened; a 

 carina encircles the body whorl on the left side; aperture small, rounded, 

 or oval, the right side in advance of the left side. 



Animal. External appearance. The body is small, the foot short, 

 rounded before and pointed behind; tentacles long and filiform; eyes 

 sessile at the inner base of the tentacles; when removed from the shell the 

 animal of Planorbis planorbis has a blackish or lead-colored mantle, a 

 yellowish liver, and a pinkish ovotestis. 



ANATOMICAL CHARACTERISTICS 

 PLATE 1 



GENITALIA. Male Organs (fig. 1). Seminal vesicle (SV) 3.5 mm. 

 long and 0.7 mm. wide, elongate-cylindrical, covered for the most part by 

 small pustule-like glands. Sperm duct (SPD) very long (14 mm.) adherent 

 to the oviduct. The prostate (PRS) is about 5 mm. long and consists of 

 forty to forty-five diverticula placed in a single row on a long prostate 

 duct (PD) which is separated from the sperm duct. Both sperm duct and 

 prostate duct enter the smaller vas deferens near the vagina (fig. 1, YD, 

 PD). The prostate diverticula are cylindrical in form and a trifle more 

 than 0.5 mm. in length. A cross section through the prostate and oviduct 

 shows the relationship between the sperm duct and the prostate duct 

 (fig. 7). The vas deferens is a long (12 mm.) narrow tube (VD). 



The penial complex is elongated (fig. 2), the preputium (PR) is long 

 (3 mm.), cylindrical, and the vergic sac (VS) is short (0.7 mm.) and some- 

 what less in diameter than the preputimn. There is one long and narrow 

 retractor muscle (R^M) attached to the vergic sac near the junction of the 

 latter with the preputium. A group of five or more small muscles near the 

 base of the preputium and a longer, narrow muscle attached to the upper 

 part of the preputium have been called supporting muscles (SM) . They are 

 not attached to the columella muscle but to the fore part of the head. The 

 long, narrow muscle may play a part in retracting the preputium after 

 copulation. 



Internally (fig. 4) the preputium has two vertical pilasters and a large 

 number of longitudinal muscular ridges (PL). The walls of the preputium 

 are thin but the walls of the vergic sac are thickened, especially at the 

 summit where the vas deferens enters. The verge (V) is short and wide in 

 repose and nearly fills the vergic sac. A section through the verge and a 



