430 GASTEROPODA OF THE INFERIOR OOLITE. 



Defrance, in constituting the genus Pl&urotomaria, applied the name " ornata " to 

 quite a different species (vide infra). This was accepted by Morris, who 

 accordingly retained the name "Pallium" for Sowerby's species, and Tawney 

 followed suit. It is now proposed to restore Sowerby's specific name. 



Description (Sherborne variety) : 



Height . . . . .30 mm. 



Basal diameter . . . .42 mm. 



Spiral angle ..... 90°. 



Shell turbinate, subdepressed, umbilicate. Spire regular, apex pointed. 

 Whorls (six to seven) angular to subconvex 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 costas 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 PI. 

 tuberculosa, though without doubt the species recognised in the Oruata-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 Ornatse generally, seem to connect PI. ornata, Sow., 

 with some of the Granulatae, more especially with PI. granulata, Sow. 



The type was from Dundry. The variety above described is abundant in the 

 /SVn/.jr/-()('(| at Oborne. Very characteristic specimens, obtained from Dundry, 

 are to be seeti in tin' Bristol Museum These have somewhat bolder ornaments 

 than the figured specimen, but in other respects agree 



