GASTEEOPODA. 



appearance of a tMn. ooluinella with a deep umbilicus. P. 

 dumosum is spiniferous ; P. subrectum is simply bent or arcuate. 

 Distribution, 46 species. Silurian — Carboniferous. Europe, 

 NortL. America. 



Family IX. — Ttjbbin-id^* 



Includes Phasiai^ella (p. 263), Imperator (p. 264), Tubbo 

 (p. 263), with, the following sub-genera : — 



Callopoma, Gray* Distinguished by the extreme complexity 

 of the operculum. '* The opercula of G. fluduosum, Gray (Turbo) 

 (Maz.), are flat, and covered with a dark horny layer inside, dis- 

 playing about 6 whorls. Outside with a broad, central, spiral 

 callus, white and granular, concealing the umbilicus, with 

 extremely minute pustules oyer the surface, sometimes with a 

 few sharp prickles. A deeply cut groove surrounds the callus, 

 followed by a green, plaited, spiral frill prickly inside. Between 

 this and the outer margin are 4 — 6 fine emerald necklaces, sup- 

 ported on slender spiral ribs, with deeply channeled interspaces. 

 The operculum of 0. saxosum, inhabiting Panama, is formed on 

 a much coarser plan." — (P. Carpenter.) 



Uvanilla, Gray. Example, U. oZ^'vaeea, Mexico. 



Distinguished by the absence of an umbilicus, and the bi- 

 ridged operculum. 



Distrihution, 3 species. Mazatlan, Mexico. 



Phasianella. 

 Sub-genus, Eucosmia, P. Carpenter, 1864. 

 Etymology, eu, well, and cosmia, adorned. 

 Shell solid, variegated as in Fhasianella ; aperture and whorls 

 round ; axis umhilicated. 



Distrihution, 4 species. Cape St. Lucas. 



Tbochus. 



With the following sub-genera and sections : — 



Margarita, Leach (p. 265). Example, T. helicinus, Tabr. 

 Shell small, pearly, and umbilicated ; lateral cirri, 3 — 7 in. 

 British species. No typical Trochi appear to inhabit North-East 

 America, only those of this section. 3 species, Britain. 



Gihhula, Leach (p. 265). Example, T. magus, Linne. Shell 

 low- spired and imibiHcated ; lateral cirri, 3 on each side in the 

 British species. 



Circulus, Jeffreys. Shell very small, nearly flat-spired, with 

 an exceedingly wide and open umbilicus. Example, Delphinula 



* See p. 263. 



35 



