130 AMERICAN JOURNAL 



ly, SO far as the characters given would indicate, the species do 

 not diifer subgenerically from those forms of Hepfadactylus. As 

 it might be replied that the dentiform lobes between the digitations 

 were also considered as digitations, it is not superfluous to add that 

 the species of Harpago have similar dentiform lobes. The Adams- 

 ian groups are indeed natural, but in spite of their diagnoses. The 

 value of those groups is by no means equal, however. It is quite 

 true that there may be great inequality in the value of natural 

 genera, and that some naturalists would recognize genera in the 

 Pterocerce of the lamhis form on the one hand, and those of the 

 scorjjw and miUipeda on the other, or, indeed, in each form. This 

 would be a simple question of appreciation of values ; the present 

 writer is indisposed to regard the difl"erences as of generic im- 

 portance. 



Mr. Gabb's combination of the rugose Pterocerce with the spe- 

 cies of Harpago in a single genus contradistinguished from the 

 Pterocei'ce -with, smooth lips, it must be confessed, was not a happy 

 modification, as that able naturalist, on reconsideration, would 

 doubtless admit. 



In pursuance of the views explained, the Lamarckian Pterocerce 

 will therefore be re-distributed among two genera, on the bases 

 already indicated and as set forth in the following diagnoses. 



The differences in the dentition of the radula between the 

 genera are immaterial, but so are those between the Pterocerce 

 and the Strombi, as defined ; it is possible that the apparent 

 differences between the two may be still further reduced or 

 altogether nullified by the examination of other species. 



§ 5. Descriptive. 



PTEROCERA, Lamarck. 

 Historical Synonymy. 

 Aporrhais^ sp. Aldrovandi, De Test. pp. 343, 344. 

 Radix hryonice, sp. Klein, Tent. Meth. Ostrac. 1753, p. 79. 

 Heptadactylus, sp. Klein, op. cit. p. 99. 

 Millipes, sp. Klein, op. cit. p. 99. 



Binomial Synonymy. 

 K,Stromhus, Humphrey, Mus. Calonn. 1798, p. 39. (Not limited 



by description.) 

 <,Pterocera, Lam., Prod. 1799, p. 72 ; Syst. An. sans Vert. 



1801, p. 80. (P. lamhis.) 

 <,Pteroceres, Montf., Conch. Syst. ii, 1810, p. 606. (P. scorpio) 

 <,Digitata. Fabr., Fort. 1822, p. 86. 

 "^Pterocera {Millipes), Morch, Cat. Yoldi, i, 1852, p. 60. (Not 



described.) 



