GASTEROPODA. 147 



large and thick, like haliotis, but entirely covered by the tkick, hard, plaited 

 mantle of the animal. 



Stomatia (Helbliu), Lamarck. 

 Etym., stoma, the aperture. 

 Ti/pe, S. phymotis, PI. X., fig. 22. 



Shell like haliotis, but without perforations, their place being occupied by 

 a simple fm-row ; surface rugose, spirally ridged ■ spire small, prominent 

 aperture large, oblong, outer margin ii'regular. 



Distr., 12 sp. Java, Philippines, Torres Straits, Pacific, Under stones 

 at low water (Cuming). 



Fossil. M. D'Orbigny refers to this genus IS sp., ranging from the L. 

 Silui-ian to the chalk, N. America, Eui-ope. 



SCISSURELLA, D'Orb. 

 Etym., diminutive of scissus, slit. 



Type, S. crispata, PL X., fig. 23. Syn,, anatomus, Montf. 

 Shell minute, thin, not pearly ; body-whirl large ; spii-e small ; surface 

 striated ; aperture rounded, with a slit in the margin of the outer lip. Oper- 

 culate. 



Distr., 5 sp. Norway, Brit., Medit. In 7 fathoms water off the Orkneys, 

 and in deep water east of the Zetland Isles. 

 Fossil, 4 sp. Miocene — . Brit., Sicily. 



Pleurotomaria, Defrance. 

 Etym., pleura, side, and tome, notch. 

 Type, P. anglica, PI. X., fig. 24. 



Shell, trochiform, solid, few -whirled, with the surface variously ornamented ; 

 apertm'e sub-quadi'ate, with a deep slit in its outer margin. The part of the 

 slit which has been progressively filled up, forms a band round the whirls. 



Fossil, 400 sp. Lower silm-ian — chalk. N. America, Europe, Australia. 

 Specimens from clay strata retain their nacreous inner layers, those from the 

 chalk and limestones have lost them, or they are replaced by crystalline spar. 

 Pleurotomarife with wavy bands of colour have been obtained in the carb. 

 limestone of Lancashire. In this extensive group there are some species 

 which rival the living turbines in magnitude and solidity, whilst others are as 

 frail as ianthina. 



Sub-genus. Scalites, Conrad (== raphistoma. Hall.) E.g., S. angulatus 

 and stamineus. L. silurian. New York. Shell thin ; whirls angular, flat 

 above (tabulated), 8 sp. L. silurian — carb. Poly-tremaria, D'Orb., is 

 founded on P. catenata, Koninck, in which the margins of the slit are wavy, 

 converting it into a series of perforations. 



MuRCHTsoNiA, D'Arcliiac. 

 Etym., named in honom- of Sir Roderick I. Mm-chison. 

 Type, M. bilineata. PI. X., fig. 25. 



