OF CONCUOLOOY. 61 



ticulate lateral tootli. In B. canaUculatum, tlie rliachidian 

 tooth is broader, with three denticles smaller than in B. pyrimi : 

 lateral tooth 5-denticnlate. In B. carica the rhachidian is still 

 broader and armed with five denticles in the female and six 

 in the male ; lateral tooth 5-denticulate ($) or 6-denticulate 

 ((^.) In B. jyerversum $, rhachidian 5-denticulate, lateral tooth 

 0-denticulate. 



Besides these four species, a few others have been described 

 B. carica. The four species may be arranged in two groups 

 as existing on our coast, but these appear to be all varieties of 

 upon the characters of their shells. B. carica and B. per- 

 versuni have rather thick and heavy shells, with the shoulder 

 of the whorls armed with strong spines; B. pyrum and B. 

 canaUculatum have on the contrary thin, canaliculated shells 

 with unarmed whorls and a ciliated epidermis. Those dif- 

 ferences, taken in connection Avith those to be noticed in the 

 lingual dentition, might lead ns to separate the two groups 

 generically, were it not that in the Miocene formation of our 

 Atlantic slope we find intermediate forms. For instance, the 

 B. coronatum of Conrad has the thick shell and prominent 

 conical spines of the first group in conjunction with the spiral 

 canal of the second ; B. carinatum of the same author has a 

 thin smooth shell, but no spiral canal ; and B. fusiformis has 

 a thick shell, while the whorls have neither canal nor spines. 



Fam. NASSID^. 



We regard the JVassw and their allies as forming a family 

 distinct from the Buccinidse on account of the arched form 

 and very numerous denticles of the rhachidian tooth of the 

 gual ribbon, — a constant character. 



ILYANASSA,* nov. gen. 



Type, I. OBSOLETA. 



JVassa obsoleta ; Say, Journal Academy Natural Sciences, 

 Philadelphia, II, 1822, p. 232. Bucciyium ohsoletum Gould, 

 Invert. Massachusetts, 1841, p. 808, f. 210. 

 Shell reticulated or decussated, rather thick and strono- • 

 spire elevated ; inner lip smooth ; callus moderate. Foot 

 broad, without caudal bifurcation or cirri. Operculumf re- 

 sembling somewhat that of Buccinum, obovate, broadest 

 below ; nucleus a little within the margin at the outer side 

 near the base ; margin entire, not serrated ; lingual teeth 

 (plate 9, fig. J.l,)like thoseof A^ifssf/. Ova-capsules (plate 9, fig_ 



*Etym., Ihv;, limus ; avaara, regina. 



t The operculum is always herein considered in its natural position 

 when retracted into the aperture of the shell. 



