TROCHUS. 529 



Margarita undulata, Sowerby, Malacalog. Magaz. p. 26 ; Conch. Illust. Margar. 



f. 4. — Gould, Invert. Massach. p. 254, f. 172.* — 



Reeve, Conch. System, pi. 221, f. 4. 

 Turbo incarnatus, Couthouy, Boston Jl. Nat. Hist. vol. ii. p. 98, pi. 3, f. 13. 



By regarding Margarita as only a section of this genus, 

 we are compelled to prefer the later, but more characteristic 

 designation of Sowerby, to that bestowed by Lowe upon 

 the young of this species, since the epithet carneus has 

 already been assigned to a Trochus in the pages of 

 Gmelin. The occasional entire or partial absence of the 

 spiral sculpture is a remarkable feature of this widely 

 diffused and variable species. The shape in general is 

 suborbicular and depressed conical ; in large foreign ex- 

 amples it is sometimes almost conoidal ; the lateral outlines 

 are more or less arched. The texture is not particularly 

 thin, but in most individuals (from our own shores) is a 

 little translucent ; the surface is but moderately lustrous, 

 and of an uniform colour, ranging in tint from a slightly 

 empurpled rose to yellowish flesh-colour : the fry are quite 

 white, hence the apex of the adult is usually of a paler 

 cast than the rest of the exterior. Numerous short and 

 wavy longitudinal folds emanate from beneath the strongly 

 impressed, and often subcanaliculated, sutures, and densely 

 disposed spiral costellae, that in general are broader than 

 their intervals, each interstice being almost immediately 

 filled up by a narrower riblet, for the most part encircle 

 the upper area of the shell ; the lower surface being either 

 smooth or merely traversed by more or less obsoletcly 

 raised spiral strise. In one of our varieties the entire shell 

 is destitute of costellse ; in another the upper portion of 

 the body- whorl alone is free from them ; the folds, how- 

 ever, are present in both. The riblets are sometimes pro- 

 minent and rounded, sometimes plano-convex ; occasionally 



VOL. II. 3 Y 



