CHTHAMALUS STELLATUS. 457 



Corea. The shells when crowded, are rendered cylindrical, and 

 more or less elongated, with the sutures as viewed externally quite 

 obliterated ; the surface rugged and much disintegrated ; and the orifice 

 nearly circular: in this extreme condition I have seen specimens from 

 England, from near Genoa, and from the mouth of the Plata : the 

 specimens from these last two localities were of remarkable size, being 

 half an inch in diameter, and rather more than half an inch in height. 

 Again, other British specimens (fig. lc), though not nearly so common, are 

 rather steeply conical, and have not only their sutures distinct, but narrow 

 radii are plainly developed on apparentlyboth sides of the sutures; in this 

 case the orifice is slightly toothed, and is rather elongated : I have seen 

 specimens in this condition, but with their walls rather more deeply 

 folded, from the Cape de Verde and Philippine Archipelago. Other 

 specimens, from some unknown tropical sea, differed only in the walls 

 being but slightly folded, and being so perfectly preserved as to be 

 externally covered with membrane : this latter circumstance gave the 

 specimens a peculiar appearance. In this condition were some speci- 

 mens (fig. 1 d) attached to oysters sent to me by Professor Agassiz, from 

 Charlestown ; and which differed from all the others that I have seen, in 

 the thinness and smoothness of their compartments, and in the facility 

 with which the compartments separated from each other and from the sur- 

 face of attachment : hence I have called this form, which, until finding 

 more important differences, [ must rank as a variety, fragilis : it has 

 stronger claims than the other varieties to be specifically separated ; 

 but I suspect that it has been exposed to some peculiar modifying 

 conditions. 



Lastly, we have the variety (fig. 1 b) excellently figured and described 

 by Poli, under the name of L. depressa : this is much depressed, with the 

 walls thin, not folded, with the surface much corroded, with the sutures 

 very distinct, with the radii not at all or barely developed, but with 

 the alse largely developed, and marked with lines of growth, resulting 

 from the diametric growth of the shell : the orifice is hexagonal, but 

 broadest towards the carinal end : most of the specimens, but not all, 

 have on the under sides of their compartments rugged pillars depend- 

 ing from beneath the alse, for the purpose, apparently, of supporting 

 the much depressed shell. This much depressed variety attains a 

 larger basal diameter (but not a greater bulk or internal capacity) 

 than any other variety, namely, sometimes three quarters of an inch. 

 The great peculiarities of this variety result, apparently, from its much 

 depressed form, deeply corroded not folded walls, and considerable 

 diametric growth ; from the latter cause the alae are largely developed ; 

 as I can find neither internally nor externally any fixed diagnostic 

 character I have not hesitated to rank this form as a variety. Poli 

 found his specimens mingled with the ordinary C. stellatus, on the 

 shores of Sicily ; and I collected at St. Jago, in the Cape de Verde 

 Archipelago, some specimens nearly as well characterised, also associated 

 with the common variety. 



The shell itself is dirty-white or gray, or brown : in some varieties, 

 however, the white is nearly pure : internally the parietes are generally 

 tinted dull purple. The coriurn of the sack is dark greenish-black, 



