Subfamilies, Genera, and Subgenera — Recent and Fossil 167 



1926. Planorbiirius Kennard and Woodward, Syn. Brit. Non-Marine Moll., p. 67. Type 

 Helix cornea Linn. As subgenus 



1926. Planorbis Lindholm, Archiv. fiir Mollusk., Heft 6, year 58, p. 252. Ideogenotype 



Helix cornea Linn. As genus, type by Montfort 



1927. Planorbis Pilsbry and Bequaert, Bull. Amer. Mus. N. H., LIII, pp. 115, 116. 



Type Planorbis corneus (Linn.). As genus 

 1929. Coretus (Gray 1847) H.^As, Trab. Museo Cien. Nat. Barcelona, XIII, p. 378. 



Type evidently Helix cornea Linn. As genus 

 1931. Planorbis F. C. Baker, Proc. Zool. Soc, London, p. 583. Genotype Helix cornea 



Linn. As genus 

 1931. Coretus (Andanson, 1757) Germain, Moll. Terr. Fluv. France, II, p. 517. No 



type cited but Planorbis corneus (Linn.) described. As subgenus of Planorbis 

 1931. Planorbis Thiele, Handbuch, Tcil 2, p. 479. Type Planorbis corneus (Linn.). 



Subgenus of Planorbis Miiller, 1774 



Shell (plate'80, figs. 22-24). Large, sinistral, discoidal, rather solid, of 

 few gradually enlarging whorls, equally visible above and below; aper- 

 ture slightly enlarged, in the same plane as the whorls; lips sharp, not 

 thickened. 



Animal. With short, wide foot, rounded before, tapering behind, the 

 vela area large; tentacles long, wide at the base, and tapering to a point, 

 eyes sessile at their inner bases. Color of living animal lead, sometimes 

 nearly black tinged with brown; tentacles bluish black. Sometimes the 

 whole body is reddish. 



The young snail of two whorls, recently hatched from the egg capsule, 

 is very translucent, the organs plainly visible through the hyaline shell. 

 The body shows pinkish through the shell, head and foot with border of 

 white on edge. The radula sac may be seen working backward and forward, 

 when feeding, as in the adult animal. The heart may be observed beating 

 rapidly. The young snails are distinctly physoid in form and glide about 

 like Physa. Specimens of the young with bifid tentacles are not uncommon. 



ANATOMICAL CHARACTERISTICS 

 PLATE 20 {Planorbarius corneus (Linn.) ) 



GENITALIA. Male Organs (fig. 13). The seminal vesicle (SV) is about 

 4 mm. long and 1 nun. wide, narrowing at the anterior end to the diameter 

 of the ovisperm duct. This organ is a rounded mass of small vesicles. A 

 number of small vesicles continue down one side of the ovisperm duct. The 

 sperm duct (SPD) is about 10 nnn. long. Where it leaves the ovisperm duct 

 it is of small diameter, but it gradually enlarges to twice this diameter near 

 the prostate where it abrui^tly expands to several times the first diameter, 

 and then suddenly diminishes again to almost its original diameter. The 

 prostate (PRS) is elongated and somewhat fan-shaped, 4.5 mm. long. The 

 duct of the prostate is a continuation of the vas deferens and is about 

 1 mm. long. It lies over the sperm duct with which it is connected, the 

 prostate diverticula radiating from this duct. The vas deferens (VD) is 

 a narrow tube about 12 mm. long. 



The prostate in section <fig. 4) is radiate or fan-shaped in form, the 

 seven to nine main diverticula branching several times (usually lour) 

 toward the outer part of the section. Figure 4 also shows the relationship 

 between the uterus, the nidamental gland, and the prostate, the figure being 

 a cross section cutting through these organs. The prostate diverticula may 

 be noted to enter the prostate duct directly. 



