GASTEROPODA. 147 



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

 mantle of the animal. 



STOMATIA (Helblin), Lamarck. 



Etym,, stoma, the aperture. 



Type, S. phymotis, PL X., fig. 22. 



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

 a simple furrow ; surface rugose, spirally ridged ; spire small, prominent 

 aperture large, oblong, outer margin irregular. 



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

 at low water (Cuming). 



Fossil. M. D'Orbigny refers to this genus 18 sp., ranging from the L. 

 Silurian to the chalk, N. America, Europe. 



SCISSURELLA, D'Orb. 

 Etym., diminutive of scissus, slit. 



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

 Shell minute, thin, not pearly ; body-whirl large ; spire 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. 



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

 aperture sub -quadrate, 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 silurian 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. 

 Pleurotomariae 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, IV 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'Archiac. 



Etym., named in honour of Sir Roderick I. Murchison. 

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



