80 The Molluscan Family Planorbidae 



Pilsbry (1934, p. 47) associates Taphius with Helisoma and refers 

 Taphius pronus to Helisoma together with caloderma, but pronus certainly 

 does not resemble any form of Helisoma, rather is it allied to Tropicorbis. 

 What the group may be and where it may be placed can only be deter- 

 mined by an anatomical study. With our present limited knowledge, it 

 seems best to regard Taphius as a genus related to Tropicorbis. An excel- 

 lent account of the shell variation of Taphius andecolus, accompanied by 

 a good plate, is given by Pilsbry (1924, p. 49, plate 4). 



Genus TROPICORBIS Pilsbry and Brown, 1914 



Type by original designation, Planorbis liebmanni 

 Dunker (= Pkmurbis orbiculus Morelet) 



1880. Gyrorbis Fischer and Crosse, Etudes Moll, terr-fluv. Mex. et Guat., II, p. 70 

 (non Gyrorbis Fitz., 1833). Example Planorbis orbiculus Morelet. 



1884. Menetus Tryon (non H. and A. Adams), S. and S. Conch., iii, ]>. 106. Example 

 Planorbis heloicus Orb. 



1899. Planorbula Martens (part), Biol. Cent. Amer., Moll., p. 398. Includes Planorbis 

 obstructus Morelet and Planorbis dcntiens Morelet, now referred to Tro- 

 picorbis. 



1899. Menetus M.artens (part) (non H. and A. Adams), o\^. cit., \). 390. Includes 

 species now referred to Tropicorbis. 



1914. Tropicorbis Pilsbry and Brown, Proc. Acad. Nat. Sci. Phil., 66, p. 212. Type 

 Planorbis liebmanni Dunker. As section of Planorbis. 



1921. Tropicorbis Germain, Rec. Ind. Mus., XXI, p. 91. Type incorrectly given as 

 Planorbis tnaya Morelet. As subgenus of Planorbis. 



1923. Tropicorbis Wenz, Fossil. Cat., Pars 22, p. 1627. Genotype Gyrauhis (Tropicor- 

 bis) liebmanni (Dunker). As subgenus of Gyraulus. 



1930. Tropicorbis H. B. Baker, Oc. Papers Mus. Zool. Univ. Mich., No. 210, p. 43. 



Type Planorbis liebmanni Dkr. As genus. 



1931. Tropicorbis Thiele, Handbuch, IV, Teil 2, p. 480. Type wrongly stated to be 



Planorbis maya Morelet. As section of Planorbis. 

 1934. Tropicorbis Pilsbry, Proc. Acad. Nat. Sci. Phil., 86, p. 52. Type Planorbis 



liebmanni Dunker. As genus. Anatomy described. 

 1936. Tropicorbis F. C. Baker, Nautilus, 49, p. 104. Anatomy of Planorbis obstructus 



Morelet and Planorbis havanensis Orb. described. As genus. 



1939. Oh^tructio H.\as. Zool. Ser. Field Mus. Nat. Hist. XXIV, p. 99. Type by original 



designation Planorbis janeiremsis Clessin. As subgenus of Planorbis. 



1940. Tropicorbis F. C. Baker, Nautilus, LIII, p. 106. As genus. 



1941. Obstructio Haas, Nautilus, 55, p. 31. 



Shell. Of medium size, idtradextral, orbicular, of few whorls which may 

 increase regularly in diameter (plate 77, figs. 7-9 orbiculus) or the body 

 whorl may increase rapidly in diameter (plate 77, figs. 10-12, pallidus) ; 

 whorls in view equally on both sides, somewhat overlapping on the left 

 (spire) side; aperture unarmed or with one large parietal lamella with a 

 small infraparietal below it, and four lamellae within the outer lip. The 

 labial lamellae differ principally from those of the genus Planorbula in 

 having the lower palatal lamella pointing slightly downward on the left 

 side while in Planorbula this lamella always points upward, in the group 

 Hcddemanina the upward end forming a vertical and transverse lamella 

 combined. The basal lamella in Planorbula is normally more massive and 

 is, in some species, distinctly curved (plate 76, figs. 7, 8, 9). 



