GASTEEOPODA. 



Distribution, 7 species. Jurassic and Cretaceous. Trance, 

 Switzerland, Germany. 



Plajntaxis. M. Deshayes places this genus in Littorinidce, 

 but Dr. Macdonald states that it is anatomically closely related 

 to Cerithium, the lingual teeth are similar, and that the audi- 

 tory sacs contain spherical otoliths. 



Quoyia, Deshayes, 1830. 



Dedicated to the celebrated naturalist to the Astrolabe. 



Synonyms, Fissilabria, Brown ; Leucostoma, Swainson. 



Shell solid, elongated, conical, apex decollated; whorls flat, 

 the body whorl sub-angular at the base ; aperture small, semi- 

 lunar, produced in front; columella thick, curved, truncated 

 anteriorly, with a spiral fold posteriorly, operculum horny, 

 paucispiral, nucleus lateral. 



Distribution, 2 species. New Guinea, Cochin China. 



Fossil. Eocene, Paris (1). Miocene, Dax (1). 



The three following genera are provisionally referred to Cer- 

 thiadce. 



Ceritella, Morris and Lycett, 1850. 



Etymology, diminutive of Cerithium. 



Synonym, Tubifer (pars), Piette, 1856. 



Type, Ceritella acuta, Mor. and Lye. 



Shell turreted, subulate, spire acute ; whorls flat, margins 

 usually sulcated ; last whorl large ; aperture elongated and 

 narrow ; canal short ; columella smooth, rounded, and slightly 

 reflected at the base ; outer lip thin. 



Fossil, 17 species. Middle Jurassic strata. England, Erance. 



Brachytrema, Morris and Lycett, 1850. 



Etymology, brachyos, short, and tremos, a cut. 



Examples, B. Buvignieri, Mor. and Lye, 

 E. Wrightii, Cotteau (Fig. 13). 



Shell small, turreted, turbinated ; whorls either 

 costated, nodulated, or cancellated; the last whorl 

 large and ventricose ; columella smooth, rounded, 

 twisted near its base, and reflecting outwards, 

 forming a short, oblique canal ; aperture 

 moderately subovate, its length being usually 

 less than that of the spire. 



Some species, as B. varicosa and B. pygmcea, 

 acquired at certain arrests of growth thickened 

 outer lips or varices, as in Triton. 



