SMITH : NOMENCLATURE OF CERTAIN GENERA. 335 



relationship to the greatly developed mantle, (3) the presence 

 of only an upper jaw in the mouth, and (4) slight differences in 

 the radula. This subject has been fully treated of, many years 

 ago, by Troschel in Wiegmann's Archiv f. Naturgeschichte, 

 1839, pp. 177-184, pi. V. f. 8. (radula). 



PH Y s A. 



This genus was founded by Draparnaud in 1801 (Tab. 

 Moll. terr. et fluv. France, p. 52) and not by Lamarck as stated 

 by Jeffreys and in the Conchological Society's list. 



P. fotitinalis (Linn.) is the first species quoted by 

 Draparnaud; and may therefore be re*garded as the type of the 

 genus. This in the Conchological Society's Hst is placed in the 

 section Bidinus. This location is erroneous, as it does not 

 possess the essential characters of that group. 



Adanson^ (the author of the genus) distinctly states 

 that the mantle does not extend beyond the border of the 

 aperture of the shell, whereas in P. fontinalis the digitate pro- 

 longations are very remarkable. 



The animal of Bulinus has been studied by Jickeli- and 

 he discovered that, both as regards the jaw and radula, it has a 

 much closer affinity with Planorbis than with Physa. 



The second British species {P. hypnorum) forms the type of 

 Fleming's^ genus Aplexa^ distinguished from Physa merely 

 on account of the mantle being neither digitate nor expanded. 

 This character alone, however, seems scarcely of generic 

 importance, and therefore I should be inclined to regard Aplexa 

 as a section or sub-genus. It agrees with Bulinus as regards the 

 mantle, but differs from it in the jaw and radula, which are both 

 as in Physa. 



It is stated by Fischer ' that the etymology of Bulinus is 

 unknown ; but, it is evident that Oken, who in 1815, emended 



1 Hist. Nat. S^n^gal, Coquil. p. 6. 



2 Verhand!. Leop. Carol. Akad. Naturf. 1874, vol. xxxvii, p. 209, pi. iii, f. 1-4, 



3 British Animals, p. 276. 



4 Emended by Hermannsen to Apleeta, Indjcis Gen, Mai., p. 65, 



5 Manuel de Conch, p. 509. 



