Subfamilies, Genera, and Subgenera — Recent and Fossil 171 



Just how many species may be included in Planorbarius is somewhat 

 of a question. Germain (1921, 1931) includes one species with several 

 varieties. In the catalogue of Planorbidae in the Indian Museum, Germain 

 includes in Planorbis (= Planorbarius) several species which belong in 

 other genera, principally Afroplanorbis. 



Species Considered as Valid. Since the members of this genus are 

 extralimital, the species listed by Westerlund which appear to be referable 

 to Planorbarius are cited here. 



Planorbarius corneus (Linn.) Planorbarius metidjensis (Forbes) 



Planorbarius elophilus (Bgt.) Planorbarius stenostoma (Bgt.) 



Planorbarius kabylianus (Let.) 



Geological Distribution. According to Wenz (1923, p. 1481), the genus 

 Corneus ( = Planorbarius) begins in the late Eocene period. 



Remarks. The genus Planorbarius is at once distinguished from all 

 other groui)s of Planorbidae by characteristics of the. genitalia. The very 

 large preputium and very small vergic sac are particularly noteworthy, 

 and the form of the penial gland with its elongated appendage and the 

 very small verge are unique features of the genus. The two retractors of 

 the penial complex are also diagnostic features. The structure of the pros- 

 tate and ovotestis is likewise distinctive. No specimens with everted gland 

 or verge have been observed and one can only surmise that the gland is 

 everted as an excitatory organ and probably the small vergic sac and verge 

 are extended from the male opening, as has been observed in Helisoma. 



Almost all writers on European fresh-water Mollusca have mistaken the 

 penial gland appendage for the true penis (verge) and have completely 

 missed the small, vestigial true penis. Other authors have ignored all details 

 of the internal anatomy of the penial complex, simply figuring the large 

 pre]:)utium and the vas deferens as directly entering this organ. 



The systematic position of Planorbarius is without doubt in the sub- 

 family Helisomatinae. The presence of the penial gland and the multiple 

 character of the diverticula of both prostate and ovotestis indicate this 

 relationship. The strongly ridged kidney is also another evidence of this 

 kinship. It is the only group of the subfamilv thus far known outside of 

 America. The large shell resembles that of Helisoma especially the sub- 

 genus Pierosonia. 



The proper genus for the reception of the Helix cornea of Linn, has 

 been in some dispute. Many authors have considered it the type of the 

 genus Planorbis of Miiller. Dall (1905) considered it the type of Planorbis, 

 dating it from Montfort, 1810, who definitely established cornea as the 

 tvpe of the genus. This procedure has been followed bv Germain (1921), 

 Pilsbry and Beciuaert (1927), Lindholm (1926), Baker "( 1931) , and Thiele 

 (1931). Dall's conclusions were questioned by Kennard and Woodward 

 (1924) who maintained that the type of the genus Planorbis is the Helix 

 planorbis of Linn, by absolute tautonomy. H. B. Baker (1930) has also 

 expressed the same opinion. Germain, in a later work (1931), cites the 

 Helix planorbis of Linn, as the tvpe of Planorbis Guettard 1756 and 

 Geoff roy 1767. 



The generic name Coretus is in current use by many European con- 

 chologists. Some of these use the Coretus of Adanson 1757 (as Clessin 

 1886 and Germain 1931) but that author was non-binomial and pre- 



