GASTEKOPODA. 



appearance of a thin columella "with, a deep umbilicus. P. 

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

 Distribution, 46 species. Silurian — Carboniferous. Europe, 

 North America. 



PAMILY IX. — TUEBINIDiE* 



Includes Phasiakella (p. 263), Imperatob. (p. 264), Tuebo 

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



Callopoma, Gray* Distinguished by the extreme complexity 

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

 (Maz.), are flat, and coyered 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 grooye 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 C. saxosum, inhabiting Panama, is formed on 

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



Uvanilla, Gray. Example, U. oUvacea, Mexico. 



Distinguished by the absence of an umbilicus, and the bi 

 ridged operculum. 



Distribution, 3 species. Mazatlan, Mexico. 



Phasiakella. 

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

 Etymology, eu, well, and cosmia, adorned. 

 Shell solid, yariegated as in Phasianella ; aperture and whorls 

 round ; axis umbilicated. 



Distribution, 4 species. Cape St. Lucas. 



Trochus. 



With the following sub-genera and sections : — 



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

 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. 



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

 low-spired and umbilicated ; 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, Delphi nu la 



« See p. 26:3. 



35 



