MANUAL OF THE MOLLUSCA. 



Fossil, 16 species. The greater number belong to the Great 

 Oolite, others occur in the Kelloway Eock. England, Prance 



Mesostoma, Desbayes, 1864. 



Exam'ple, M. grata, Db. 



Shell elongated, turreted, scalariform ; aperture nearly cir- 

 cular, dilated, obliquely cut, terminating in front by a semi- 

 canaliculated angle ; columella sHgbtly concave, cylindrical, 

 obliquely truncated, lip simple, and slightly expanded. 



Fossil, 4 species. Eocene. Paris basin. 



[Eamilt Aporbhaidje, Gray, 1856,] 



Includes the genera Apoeehais (see p. 244), Pteeodonta, 

 Steuthiolaeia (p. 246), and TTatt a ; also 



Alaeia, Morris and Lycett, 1854. 



Synonym, Tessarolax, Gabb, 1864. 



Etymology , ala, a wing. 



Examples, Alaria trifida, Phillips, sp. ; A. cingulata, Pictet 

 and Eoux, sp. 



Shell turreted, fusiform, terminating anteriorly by a canal ; 

 wing digitated or palmated, formed by the prolongation of the 

 free border of the last whorl, and which is applied against the 

 last whorl but one, but never adheres to the rest of the spire ; 

 posterior canal wanting ; right lip without a sinus. 



Distribution, about 50 species. Jurassic. Europe, Himalaya 

 Mountains, South Africa. Cretaceous, 9 species. England, 

 Erance, Germany. 



The species of this genus have been referred to Bostellaria, 

 JPterocera, and Aporrhais. 



Diaethema, Piette. 



Shell with continuous varices. 

 Distribution. Lower Oolites. Erance. 



Pelicaria vernis, Adams, has a spiral shell ; the spire of adult 

 covered with an enamel coat ; aperture ovate ; outer lip sinuous, 

 sharp-edged. 



? Btxlimella, Hall, 1857. 



Shell more or less fusiform ; whorls convex, the last one much 

 enlarged; columella truncated; outer lip thin, with a slight 

 notch or sinus at the margin near its junction with the pillar. 



Distribution, 3 species. Carboniferous. Indiana. 

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