GASTEEOPODA. 253 



Distribution, Pliilippinos, West America. 



Fossarus (Adans.), Philippi. F. sulcatiis, PI. IX., Fig. 12. 



Synonym, Phasianema, Wood. 



Shell perforated ; inner li]3 thin ; operculum not spiral. 



Distrihntion, Mediterranean. 



Fossil, 3 species. Miocene — . Britain, Mediterranean. 



Risella, Gray. Lit., melanostoma, PL IX., Fig. 14. 



Shell trochiform, with a flat or concave base ; whorls keeled ; 

 aperture rhombic, dark or Tariegated, operculum pauci-spiral. 



Distribution, New Zealand. 



Conradia, Adams. Aperture circular. 3 species, Japanese seas. 



Couthouyia, Adams. Shell ovate, with an acute spine ; aper- 

 ture semi-oval. 1 species, Japanese seas. 



SoLAEiUM, Lam. Stair-case shell. 



Etymology, solarium, a dial. 



Synonyms, architectoma, Bolten. Philippia, Gray. Helico- 

 cryptus, D'Orbigny ? 



Type, S. perspectivum, PI. IX., Fig. 15. 



Shell orbicular, depressed ; umbilicus wide and deep ; aper- 

 ture rhombic ; peristome thin ; operculum horny, sub-spii'al. 



The spiral edges of the whorls, seen in the umbilicus, have 

 been fancifully compared to a winding stair- case. 



Distribution, 25 species. Tropical seas. Mediterranean, East 

 Africa, India, China, Japan, Australia, Pacific, West America. 



Fossil, 56 species. Eocene — . Britain, &c. 26 other species 

 (oolites — chalk) are provisionally referred to this genus ; the 

 cretaceous species are nacreous (v. trochus). 



Sub-genera. Torinia, Gray. T. cylindracea, oper- 

 culum conical, multi-spiral, with projecting edges, 

 Fig. 107. Living, New Ireland. 



Fossil, Eocene. Britain, Paris. 



Bifrontia, Desh. {Omalaxis, Desh.) S. bifrons, 

 discoidal, the last whorl disengaged. 1 recent 

 sj^ecies. Madeira. Fig. i07.« 



Fossil, 6 species. Eocene. Paris, Britain. 

 ? Orbis, Lea. Discoidal, whorls quadrate. 



Fossil, Eocene. America. 



Discohelix (calculiformis) Dunker, 1851. Lias, Gottingen. 

 This name was proposed for the depressed Euomphali of the 

 Lower Oolites, of which there are several species in Normandy 

 and England. 



« Operculum of S p^tulum,lj^v£i. -^ , from Deshayec, 



