PLEUROTOMARIA. 411 
Bibliography, §c—Sowerby’s type is at the Bristol Museum, and in all 
respects corresponds with the specimen now figured. The specimen in the 
collection of Sowerby’s types at the British Museum seems to represent a 
somewhat narrow variety of Pl. wnisulcata, dV’ Orbigny. As pointed out by Tawney, 
the whorls of Sowerby’s species are convex but not angular. This may be gathered 
both from the description and figure in the ‘ Mineral Conchology.’ The entire 
section (Leptomaria) of which Pl. sulcata may be regarded as the type-species, as 
developed in the Inferior Oolite, presents a series of forms which run into each 
other. Moreover, in such shghtly sculptured shells what little ornament there 
may have been is often modified by fossilisation, whilst the spiral angle varies so 
much that it almost ceases to be a guide. Hence the division into “ species ”’ is 
attended with unusual difficulty. 
Description : 
Height 3 : 3 ; . 22 mm. 
Basal diameter , : 3 . 32mm. 
Spiral angle (convex) . : : 5 i 
Shell heliciform and largely umbilicated. Spire convex, with an obtuse apex. 
The spire-whorls (about six) are narrow, convex or scarcely angulated, and 
separated by a suture, which in the early stages is somewhat canaliculate. The 
ornaments are faintly impressed, and vary much; specimens from Dundry 
generally show radial furrows in the upper part of the whorls, whilst the visible 
spiral ornamentation is chiefly anterior. Specimens from the Murchisonx-zone of 
Burton Bradstock exhibit spiral striz on the spire-whorls throughout, and this, 
in the apical portion, is reticulate, whilst the body-whorl is smooth, merely 
showing the growth-lines. 
The sinus-band is antero-mesial and very narrow, being situated on the most 
prominent part of the whorl; it is usually countersunk and smooth. The body- 
whorl is relatively large and smooth, the flexuous growth-lines constituting the 
only ornament ; these are continued in the rounded base to the edge of the wide 
and deep umbilicus. Aperture subovate and oblique. 
OBCONIOAL VARIETY (figs. 7, 7 a, 7 D). 
Cf. PLEUROTOMARIA OBCONICA, Tawney. Dundry Gasteropoda, p. 45 (37), 
pl. iii, fig. 6. 
Cf. also PLEUROTOMARIA LHVIGATA, Deslongchamps. Vol. cit., p. 188, pl. xvii, fig. 7. 
The general outline is that of a blunt cone, the spire being convex and the 
spiral angle ranging from 80° to 85°. Most of the specimens which I have 
