366 BULLETIN OF THE 



small, oval, posterior, concealing a shell : no longitudinal furrows above the 

 margin of the foot, and no caudal mucus pore : distinct locomotive disk ? 

 external respiratory and anal orifices on the right anterior margin of the 

 mantle ; orifice of combined genital organs behind and below right eye-peduncle. 



Shell internal, sigaretiform, rudimentary, small, flat, oblong, subspiral, 

 nucleus infero-posterior. 



Jaw ribbed. 



Lingual membrane 1 



Brazil. 



Until the jaw and dentition be known, its position is uncertain. The former 

 from one of Ferussac's figures seems to be costate. 



For figure of animal, see Ferussac, Hist., PI. YII. A. 



From Ferussac's figure 4 it appears probable that the shell may be more 

 properly described as external, but covered by an accessory process of the 

 mantle. 



Cryptostrakon, "W. G. Binx. Animal limaciform, subcylindrical, atten- 

 uated behind : tentacles simple : mantle slightly anterior, thin, small, conceal- 

 ing the shell : no longitudinal furrows above the margin of the foot, and no 

 caudal mucus pore : distinct locomotive disk ? external respiratory and anal 

 orifice.s on the right central margin of the mantle : orifice of genital organs ? 



Shell internal, sigaretiform, rudimentary, large as mantle, membranous, sub- 

 spiral, with postero-lateral nucleus. 



Jaw ribbed. 



Lingual membrane with tricuspid central teeth, bicuspid laterals, and quad- 

 rate marginals. 



Costa Rica. 



For figure of animal, internal shell, jaw, and lingual dentition, see Ann. of 

 N. Y. Acad. Nat. Sci., I., PI. XL 



Gaeotds, Shuttl. Animal limaciform, with greatly expanding, flat sides : 

 tentacles simple : mantle with an appendiculate process on the right posterior 

 margin under the spire of the shell, which is internal, concealed before by a 

 reflection of the mantle, and behind is imbedded in the mantle : longitudinal 

 furrows ? caudal pore ? distinct locomotive disk? external respira- 

 tory and anal orifices at the right posterior margin of the mantle : orifice of 

 generative organs ? 



Shell internal, rudimentarj', thin, subspiral, .sigaretiform. 



Jaw with numerous delicate ribs, as in Cylindrella. 



Lingual membrane with peculiar, long, narrow teeth, centrals bluntly tri- 

 cuspid, laterals and marginals bluntly tricuspid. 



Porto Rico. 



For figure of the shell, see Genera of Recent Mollusca, PI. LXXII. Fig. 6 a ; 

 for jaw and lingual membrane, see Ann. Lye. Nat. Hist, of N. Y., X., PI. XL; 

 for description of animal, see Shuttleworth, Bern Mit., 1854, p. 34. 



The appendiculate mantle and position of the respiratory and anal orifice 

 distinguish it from Peltella, and the jaw seems different. 



