292 TROCHID^E. 



both hemispheres. The operculum is calcareous, and 

 of the same consistence as that of Cyclostoma ; but this 

 is multispiral and has a central nucleus. C. ? costula- 

 tum may therefore belong to the Turbinida. The shell 

 is remarkably solid for its size (three-fourths of a line in 

 breadth) , and has strong and partly dichotomous trans- 

 verse ribs ; the peristome is continuous. The very little 

 that we know of the animal is derived from Moller, who 

 states that it is allied to that of Margarita, but differs 

 in the foot of this mollusk being furnished in front with 

 filaments. Molleria would be a suitable name for the 

 genus to which the shell in question may hereafter be 

 assigned. Moller was the Danish governor of East or 

 old Greenland ; and, without neglecting his duties, he 

 did much to elucidate the history of the glacial epoch, 

 by investigating the existing mollusca of the far north. 



Genus II. TROCHUS *, Rondeletius. PL VII. f. 4. 



BODY of various sizes, but not minute : head prominent and 

 stout : foot ridged on the upper part of each side by a digi- 

 tated or fringed membrane. 



SHELL conical, with an angular periphery, highly nacreous : 

 spirt more or less raised : mouth placed obliquely ; lips or 

 edges disunited on the columellar side : umbilicus (if present) 

 variable in extent, even in the same species. 



Rondeletius called this kind of shell a Trochus, because 

 of its similarity to a Roman boy's plaything of that name. 

 His comparison would be correct if " trochus " meant a 

 top; but the word (derived from the Greek rpo^o^) is ren- 

 dered in all the best dictionaries " a trundling-hoop for 

 children." " Turbo " is the ancient name of a playing- 

 top. The shells now about to be described were (and per- 

 * Top-shell. 



