270 MANUAL OF THE MOLLUSCA. 
7 fathoms water off the Orkneys, and in deep water east of the 
Zetland Isles. 
Fossil, 4 species. Tertiary—. Britain Sicily. 
PLEUROTOMARIA, Defrance 
Etymology, pleura, side, and tome, notch. 
Type, P. anglica, Pl. X., Fig. 24. 
Shell trochiform, solid, few-whorled, 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 whorls. 
Distribution, 2 species. One occurs in deep water in West 
Indian seas. 
Fossil, 400 species. Lower Silurian—Chalk. North 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. 
Pleurotomarie 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 magni- 
tude and solidity, whilst others are as frail as ianthina. 
Sub-genera. Scalites, Conrad, I. Silurian, New York. 
Shell thin ; whorls angular, flat above (tabulated), 8 species. 
L. Silurian—Carb. 
Polytremaria, D’Orbigny, is founded on P. catenata 
(Koninck),in which the margins of the slit are wavy, conyerting 
it into a series of perforations. 
Catantostoma (clathratum) Sandberger, 1842. Shell like 
Pleurotomaria; last whorl deflected, peristome imcomplete, 
slightly varicose, irregular. fossil, Devonian, Hifel. 
Raphistoma (angulata), Hall. lL. Silurian, United States, 
Canada. Shell depressed, outer lip sinuated. In R. compacta 
(Salter) the spire is sunk and basin-shaped, the umbilical side 
flat, and the last whorl a little disunited. 
MuURCHISONIA, D’Archiac. 
Etymology, named in honour of Sir Roderick I. Murchison. 
Type, M. bilineata, Pl. X., Fig. 25. 
Shell elongated, many-whorled ; whorls variously sculptured, 
and zoned like plewrotomaria ; aperture slightly channeled in 
front; outer lip deeply notched. 
The murchigonie are characteristic fossils of the palzeozoic 
