118 VOLUTOPSIS. 



indicate distinct origin ; we find the same species on both sides 

 of Central America in numerous instances. Perhaps I usually' 

 regard species from a somewhat more comprehensive point of 

 view than does Mr. Dall, because in the present case he is quite 

 willing (indeed does not expect otherwise) to distinguish allied 

 species except by the " sum of the characters " of a number of 

 individuals of each, whilst I regard prineipall}' those "exceptional 

 cases " where the " characters graduate towards each other " as 

 extremely damaging to their specific distinctness ; consequently, 

 whilst Mr. Dall " regards the two as perfectly distinct," I expect 

 future researches to establish their identity. In case they shall 

 be united, Martjai's name having priority, must be adopted. 



N. DECEMCOSTATA, Say. PL 48, fig. 273. 



Shell light brown, aperture usually white, sometimes brownish ; 

 encircled on the body-whorl by six to eleven ribs, which, in 

 adults are usually flattened on the top ; generally only two of 

 these ribs are visible on the spire-whorls. 



Length, 2*5-4 inches. 



Massachuscttts Bay ; Maine ; Nova Scotia, etc. 



Animal frequently' })ure white, sometimes flecked with blackish. 



See distinctive characters under preceding species. 



X. cREiJRicosTATA, Dall. PL 48, fig. 274. 



Revolving ridges flat-topped and overhanging the interspaces 

 slightly, tops of ridges impressed with one or more lines ; em- 

 bryonic whorls cylindrical, free from strong ridges ; canal scarcely 

 pi'oduced ; siphonal fasciole none or very faint. White, inider a 

 yelloAvish brown epidermis. Length, 3'5 iuches. 



Unalashka ; 100 fathoms.— W. II. Dall. 



Mr. Dall remarks that this species recalls Purpura trochlea ; 

 it is, perhaps, still more like P. succincta. 



Subgenus Volutopsis, iMiJrch. 



The shells of this division are characterized by their large 

 mouths, expanded lips, want of distinctly produced canal, etc. 

 The small operculum is (in V. Noi-vegica) more ovate than in 

 the true Neptuncic ; the dentition also, varies from the typical 

 form. Volutojjsis appears to stand between Neptunea and 

 Buccinum. 



