168 CLASS III. GASTEROPODA. ORDER VII. PECTINIBRANCHIATA. 
Pl. CCXX. Fig. 10. 
Turso crassus, Wood, Index Testaceologicus, Supp., pl. 6. f. 43. 
Pl. CCXX. Fig. 11 and 12. 
Turso ruBicunDus, Nobis, Proceedings Zool. Soc., 1842. 
Cochlea rubicunda, Chemnitz, Conch., vol. v. p. 207. pl. 181. f. 1803 and 
1804. 
Turban @ robe granuleuse, Favanne. 
The rock-beaded Trochus, Humphrey. 
MARGARITA, Leach. 
Testa turbinata, spira brevi, acuta; anfractibus rotundis, umbilicum am- 
plum svepissimé formantibus ; apertura orbiculari, marginibus dis- 
junctis, labro simplici, tenui, acuto. Operculum corneum, spirale. 
The genus Margarita was instituted by Leach, and is so nearly allied 
to Trochus, that we should hardly have thought it necessary to adopt it, 
had it not been that the interesting number of shells lately referred to 
this little group by King and Sowerby exhibit a peculiarity of character 
throughout by which they may be readily identified. The greatest vari- 
ation of character in the shells of the Margarit appears to be in the 
presence or absence of an umbilicus ; for whilst some of them offer no 
trace of being umbilicated, there are many in which the umbilicus is so 
large that they look more like the land Cyclostomata. 
The shell of Margarita may be further described as being turbinated, 
and having a short, sharp-pointed spire; the aperture is orbicular, and 
the margins are disjoined, with the lip thin, simple and acute. The oper- 
culum is horny and spiral. 
Examples. 
Pl. CCXXI. Fig. 1. 
Margarita suLcata, Sowerby, Conch. Illus. Cat., No. 11. 
