430 GASTEROPODA OF THE INFERIOR OOLITE. 
** ovnata” to 
quite a different species (vide infra). This was accepted by Morris, who 
accordingly retained the name “ Palliwm”’ for Sowerby’s species, and Tawney 
followed suit. It is now proposed to restore Sowerby’s specific name. 
Description (Sherborne variety) : 
Defrance, in constituting the genus Plewrotomaria, applied the name 
Height . ‘ : : . 30 mm. 
Basal diameter : : ; . 42 mm. 
Spiral angle . : 5 SOR 
Shell turbinate, subdepressed, umbilicate. Spire regular, apex pointed. 
Whorls (six to seven) angular to subconyex and increasing by steps; sutures 
canaliculate. On the flattened posterior area of all the whorls is a system of close 
tubercular undulations drawn out radially, whilst the spiral ornamentation is 
rather faint ; in some specimens an anterior crenulated belt is developed. 
The sinus-band is median, flat and retreating in the upper whorls, rounder and 
more prominent in the lower ones; it is mostly without markings other than the 
usual sinuous growth-lines. The body-whorl is large and subconvex, with the 
undulating radial costz on the posterior area well developed, and sometimes the 
prominence of the sinus-band almost constitutes a keel; it is bluntly angular at 
the periphery, which is subcrenulate to smooth in many of the Sherborne 
specimens. Base convex, with radial ornamentation preponderating over the 
spiral; umbilicus rather small. Aperture oval-depressed. 
Varieties.—The Sherborne specimens present many varieties amongst them- 
selves, some being less glabrous and with more marginal crenulation than the one 
figured. From other districts are specimens in which the whorls are more angular, 
the tuberculations wider apart, and the base rather flatter with well-marked spiral 
ornament. On the other hand, the Sherborne variety develops glabrous forms 
where the whorls are smooth-convex, the base tumid, and the umbilicus almost nil. 
Relations and Distribution —Pl. ornata, Sow., is essentially a small form, rarely 
exceeding 30 mm. in height. It can hardly be regarded as the young of Pl. 
tuberculosa, though without doubt the species recognised in the Ornata-group 
have a tendency to inosculate. On the other hand, the narrow and prominent 
character of the sinus-band in the body-whorl, and the rounding off of the whorls, 
so different from that of the Ornate generally, seem to connect Pl. ornata, Sow., 
with some of the Granulatw, more especially with Pl. granulata, Sow. 
The type was from Dundry. The variety above described is abundant in the 
Sauzei-bed at Oborne. Very characteristic specimens, obtained from Dundry, 
are to be seen in the Bristol Museum. These have somewhat bolder ornaments 
than the figured specimen, but in other respects agree. 
