GASTEROPODA. 
Distribution, 7 species. Jurassic and Cretaceous. France, 
Switzerland, Germany. 
PLANAXIS. M. Deshayes places this genus in Littorinide, 
but Dr. Macdonald states that it is anatomically closely related 
to Cerithiwm, the lingual teeth are aoe and that the audi- 
tory sacs contain spherical otoliths. 
Quoyi1A, 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 hicks curved, truncated 
anteriorly, with a spiral fold posteriorly, operculum horny, 
paucispiral, nucleus lateral. 
Distribution, 2 species. New Guinea, Cochin China. 
Fossil. Hocene, Paris (1). Miocene, Dax (1). 
The three following genera are provisionally referred to Cer- 
thiade. 
CERITELLA, Morris and Lycett, 1850. 
Etymology, diminutive of Cerithiwm. 
Synonym, Tubifer (pars), Piette, 1856. 
Type, Ceritella acuta, Mor. and Lyc. 
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, France. 
BRACHYTREMA, Morris and Lycett, 1850. 
Etymology, brachyos, short, and tremos, a cut. 
\ Hxamples, B. Buvignieri, Mor. and Lyc., 
PR. Wrighti, 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 subovyate, its length being usually 
less than that of the spire. @ 
{ Some species, as B. varicosa and B. pygmea, Fig. 13, 
acquired at certain arrests of growth thickened Brack ans 
uter lips or varices, as in T'riton. eae 
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