396 PLEUROTOMID.E. 



crowded on the base as well as on the top or upper shelf of 

 each whorl ; the second whorl has only three of these spiral 

 striae, and two are more prominent than the rest on all the 

 top whorls ; on the third whorl and the top of the fonrth the 

 longitudinal ribs and spiral striae, being equal in size, intersect 

 each other and j^roduce a cancellated appearance, the interspaces 

 being excavated ; the points of junction on the edge of the 

 shelf at the top of each whorl are slightly nodulous ; micro- 

 scopic lines of growth slight : colour milk-white or tinted with 

 yellow: spire remarkably turreted or scalar, gradually 

 tapering to a small but truncated point : whorls 7-8, convex, 

 each having on the upper part a wide step-like shelf, which is 

 strongly angulated ; the last whorl occupies four-sevenths of 

 the shell : suture not deep, but well defined by a wavy line : 

 mouth oblong, angular above; length three-sevenths of the 

 shell : canal short and wide, nearly straight, ending in an 

 obliquely rounded notch : outer lip angular at the top, and 

 sloping downwards with a gentle curve ; edge slightly crenel- 

 lated by the points of the spiral striae : labial notch small, 

 having its greatest depth in the angle of the infrasutural shelf: 

 iyiner lip rather large, presenting (as usual in this section of 

 Plevrotoma) a smooth and polished sui'face ; pillar broad and 

 flexuous, sloping inwards to a rather sharp edge : operculum 

 ear-shaped and elongated, marked lengthwise by a furrow on 

 the inner or pillar side, and sometimes by one or two slight 

 stria) in the same direction ; layers of growth numerous and 

 oblique ; nucleus at the base, on the inner side. L. 0*65. 

 B. 0-25. 



Yar. rosea. Fleshcolour or reddish-brown. Tritonium 

 roseum (Sars), Loven, Ind. Moll. Scand. p. 12. 



Habitat : Sand, at various depths^ in the Bristol 

 Channel, and in the western, eastern, and northern parts 

 of England and Wales, and on all the Irish, Scotch, and 

 Zetlandic coasts. Donovan gives Brighton and Wey- 

 mouth as localities; but I am not satisfied that this 

 species has been found in any of our southern counties. 

 The variety is from Oban. P. turricula has been noticed 

 in all our quaternary deposits (including that at Selsea), 

 and in the Norwich and Bed Crag ; Uddevalla (J. G. J.); 

 Canada (Dawson) . Its present range is mostly northern, 



