GASTEROPODA. 



Distribution, 7 species. Jurassic and Cretaceous. France, 

 Switzerland, Germany. 



Pla^axis. M. Deshayes places tliis 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. 



QiroYiA, 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. 



Ceeitella, 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 li]D thin. 



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



BEACHYTEEiiA, Morris and Lycett, 1850. 



Etymology, brachyos, short, and fremos, 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. pygmtsa, -pig. isT 

 acquired at certain arrests of growth thickened Brachytrema 



, T • • m -i Wrightn. 



outer iips or varices, as in Triton, 



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