﻿PROSOBR AN CHI ATA. 



283 



No. 208. Pleurotoma simillima. F. E. Edwards. Tab. XXX, fig. 4, a — c. 



P. testa elongato-fusiformi, sub-lurritd, costettatd, omnino spiraliter lineaid : spird 

 elatd, acuminata: anfractibus convexiusculis, ad humeros obtuse angulatis ; postice concavis, 

 marginatis ; costettis numerosis, angustis, sub-rectis; lineis spiralibus confer lis, filif or mibus, 

 irregularibus aperturd ovali, in canali longo exeunti ; labro arcuato ; sinu lato, medio- 

 criter prof undo, sub-trigono, ad humcrum collocato. 



Var. crassilinea ; testa anfractibus acute angulatis, tribus vet quatuor lineis supra 

 medias partes cinctis. 



A long, narrow, fusiform shell, ribbed and covered with elevated spiral lines : spire 

 sub-turreted, pointed, equalling the aperture in length ; whorls, seven or eight 

 exclusive of the pullus, slightly convex, bluntly angulated at the shoulders, hollowed 

 round the posterior margins and thickened at the sutural edges, which are bordered 

 by one or two prominent raised lines. The ribs are numerous, narrow, nearly 

 straight, short, not extending beyond the middle of the whorls, and becoming obsolete 

 on the last whorl of the mature shell ; the spiral lines are closely set, fine, thread-like 

 and regular over the margins and shoulders of the whorls, but over the middle 

 these lines alternate with others still more slender. The aperture is oval and 

 produced in front into a long, narrowish, and nearly straight canal ; the outer lip is 

 arched, and presents at the posterior part on the shoulder of the whorl, a very wide 

 and moderately deep sinus, triangular in shape. 



In the variety noticed, the whorls are more sharply angulated, and they present 

 over the middle, three or four coarse, elevated lines, with an occasional intervening 

 slender line ; but in other respects the shells agree with the typical form. 



In the general aspect the present species closely resembles P. Prestioichii ; but it 

 may be distinguished from it by the turreted spire, the depressed concave posterior 

 margins and the less convex sides of the whorls, and especially by the character of the 

 longitudinal ribs, which are more numerous, straighter, and narrower, and do not 

 extend backwards beyond the shoulders ; whereas the coarse, obliquely curved ribs in 

 P. Prestwichii reach up to the very suture ; and the transverse lineation is also of a 

 finer character. From P. Wether ellii, to which it also approaches, the present 

 species is separated by the more slender form, the more vertical ribs, and the 

 narrower posterior margins of the whorls. 



Size. — Axis, rather more than 1 inch; diameter, 4-12ths of an inch. 



Localities. — Highgate, Potter's Bar, Hampstead, Muswell Hill. Southampton, 

 Alum Bay (Stratum No. 4, Prestwich), and Clarendon, at which latter place it is 

 common. The variety occurs at Highgate, Potter's Bar, and Southampton. 



