PLEUROTOMARIA. 405 



represents an acutely conical shell with a concave spiral angle and tuberculated 

 carinas. Hence the species seems to occupy a position between PL abbreviate and 

 PL Bessina. 



I have a small specimen (PI. XXXIII, fig. 11), from the Parhinsoni-zone of 

 Burton Bradstock, which plainly shows the submarginal furrow in the base. In 

 this specimen the sinus-band is narrow and prominent ; it corresponds precisely 

 both in size and structural details with specimens from the Parkinsoni-zcme of 

 Bayeux, which are generally referred to PI. circumsulcata. The other figured 

 specimens, which are referred with some doubt to PL circumsulcata, correspond as 

 regards spiral angle and general ornamentation, but they do not show a well- 

 developed marginal furrow in the base. 



340. Pleurotomaria subglabra, sp. nov. Plate XXXIV, figs. 1 and 2. 



Descript 



ton 



Height . . . . .48 mm. 



Basal diameter . . . .55 mm. 



Spiral angle (mean) .... 68°. 



Shell acutely conical, scarcely umbilicate. Spire markedly concave. Full 

 number of whorls about eleven ; these are flat or only very slightly excavated, 

 with a very close suture. The earlier whorls are terminated by a slight basal rim 

 or carina, but in the later whorls this feature is almost effaced, although the 

 spirals at the base have somewhat larger granulations where we should expect to 

 find the basal carina ; the rest of the whorl is ornamented with fine spiral striae, 

 more or less decussated, the strias in some cases being so delicate that the shell 

 becomes almost smooth. 



The sinus-band is very anterior ; it is narrow, and more prominent in the coarsely 

 ornamented than in the finely ornamented specimens, but it is not, on the whole, a 

 conspicuous feature. The body- whorl projects somewhat beyond the angle of 

 the spire, the periphery being slightly rounded off; base flat to subconvex, with 

 spiral striae corresponding to those on the flanks of the shell. There is a small 

 umbilical hollow, but no true umbilicus. Aperture subrhomboidal and oblique, 

 with but a faint trace of the columellar notch. 



Relations and Distributions. — The concave spire serves to remove PL circmn- 

 sulcata, PL sub glabra, and PL Bessina from PL abbreviata. Yet we may expect to 

 find links in the chain. Thus PL subglabra, which is probably only a glabrous 

 variety of PL circumsulcata, constitutes an intermediate stage between PL abbreviata 



