SubjafNilies, Genera, and Subgenera— Recent and Fossil 55 



hut relatively few sjjecies which belong in this genus as now restrieted. 

 The best recognized of these are: 



Planorbis planorbis (Linn.) Planarbis atticus Bgt. 



Pln7iorbis carinntus Mi'iller l^lmiorbis sieversi Mouss. 



Planorbis aniotddi Germain Planorbis antiochianus Locard 

 Planorbis marmoratus Michaud 



Geological Distribution. Oligocene to Recent time, according to Wenz. 

 It is probable that some of the sj^ecies included in this genus by paleon- 

 tologists really belong to other grouj)s. 



Remarks. The genus Planorbis is peculiar anatomically in the form of 

 the prostate with many single diverticula and in the comparatively small 

 size of the vergic sac as compared with the preputium. The verge, also, is 

 very small, short; and wide, differing markedly in this respect (as far as 

 known) from any other group of planorbes in Europe. The nature of the 

 genitalia and the form of the shell set this group apart as a distinct genus 

 of the family Planorbidae. 



For many years, the author for this genus and the species for its type 

 have been in dispute. Some authors (Tryon 1872, 1884, Fischer 1883, 

 Baker 1902, Binney 1865, Dall 1870, Fischer and Crosse 1879) quote 

 Ciuettard as authority (Mem. Acad. Sci., p. 151, 1756). Other authors have 

 cited the genus as of ■Miiller (Verm. Hist., p. 152, 1774) with Helix cornens 

 Linn, as type (Dall 1905, Pilsbry and Bequaert 1927, Baker 1931). A few- 

 have used Guettard 1756 and ^liiller 1774 in combination with Helix 

 corneus as genotype (Germain 1921, 1931). Another group of authors have 

 cited Geoffroy (Traite Coq., Paris, p. 12. 1767) with Helix planorbis Linn, 

 as genoty])e (Kennard and Woodward, 1924, 1926). 



Guettard 1756 is pre-Linnean and also non-binomial and would appear 

 to be ruled out on these accounts. Geoffroy 1767 is post-Linnean but this 

 author was not in all cases binomial and is rejected by some students for 

 this reason. Kennard and Woodward (1924, p. 9), however, have presented 

 very convincing arguments in favor of retaining the Planorbis of this 

 atithor. The Planorbis of ]\Killer (1774) is preferred by some late writers 

 (Dall 1905, Pilsbry and Bequaert 19271, who cite the Helix corneus of 

 Linnaeus as genotype, giving ^Vlontfort 1810 (Conch. Syst., II, p. 270) as 

 the first author to select a genotype. 



However, whether Geoffroy or Miiller is selected, the genotype for both 

 is Helix planorbis Linn., the selection of which is governed by the rules of 

 tautonomy (see H. B. Baker, 1930). After reviewing the evidence very 

 carefully there seems to be no valid reason why Planorbis Geoffroy, 1767, 

 should not be used, as advocated by Kennard and Woodward (1924). The 

 Helix corneus Linn, is the genotype of Planorbariiis Froriep, 1806. The 

 name Tropidiscus Stein (1850) is in use bv several European authors 

 (Germain 1921, L. Soos 1917, A. Soos 1935,'Thiele 1931) but this name 

 is a synonym of Planorbis, having the same genotype. Helix planorbis Linn. 



Genus ANISUS Studer, 1820 (Gray, 1847) 

 Type Helix spirorbis Linn, selected b}' Gra}- in 1847 



1820. Anisus Studer, Natursvis. Anzeiger Allg. Schweiz. Ges. Gesammt. Xaturwiss., 



3te Jahrg., Xr. 12, p. 91. 

 1840. Spirorbis Sw.mxson, Treat. Malac, p. 337. Tyjic Planorbis vulgaris Swain. Not 



Spirorbis Daudin, 1800 (Vermes). 



