﻿PROSOBRANCHIATA. 



319 



a series of very small, closely set, regular, rounded tubercles, frequently lost on the 

 last whorl of the adult shell ; the posterior margins are channelled and bordered 

 round the suture by a single elevated, sharp, ridge-like line, the space between which 

 and the suture is smooth ; the body whorl is nearly straight-sided, and tapers 

 gradually towards the front, assuming a nearly conical shape, and it terminates in 

 a wide and indistinct canal, slightly notched at the extremity. The aperture is narrow, 

 and of an oblong-oval shape ; the outer lip very slightly arched, thin and sharp 

 on the edge, and plicated within ; and the sinus, which is wide, very shallow, and sub- 

 trigonal in form, is placed in the margin of the whorl. 



This Pleurotoma, in its general aspect, presents a very close analogy with P. 

 conoides, of which, on a cursory inspection, it might be regarded as a variety merely. 

 It is, however, a broader shell, the spire is not so much produced, and the sculpture 

 consists of simple, transverse lineation, without the denticulated, longitudinal plication 

 which distinguishes that species ; the outer lip also is much less arched, and the sinus 

 is wider, shallower, and more triangular. 



Size. — Axis, 7-12ths of an inch ; diameter, 3-12ths of an inch. 



Locality. — •Highcliff. 



No. 244. Pleurotoma helicoides. F. E. Edward*. Tab. XXXII, fig. 7, a, b. 

 Pleurotoma turrella. Morr. 1854. Cat. Brit. Foss., p. 2/0 (non Lam.). 



P. testa elongato-fusiformi, angustd, transversim lineatd: spird elevafd, sub-conicd, 

 acuminata: anfractibus nuincrosis, ad humcros et prope suturam bi-carinatis ; marginibm 

 posticis latiusculis, paululo declivis, sub-rectis; ultimo anfractu brevi, convcxinscido, in canali 

 paiulo indistincto exeunte, ad extremitatem profunde emarginato ; lineis transversis omnii/u 

 lineis increments eleganter clathratis ; supra margines posficas crebis, exilismnis, regit- 

 laribus ; caterum elevatis, acutis, irregidaribus : aperturd angusto-ovali ; labro arcuato ; 

 sinu lato, brevi, triangulari, anticd in margine collocato. 



Shell long, narrow, fusiform, transversely lined : the spire nearly conical, pointed, 

 and much elevated, being almost twice the length of the aperture. The whorls, nine 

 or ten in number, present a narrow, elevated keel round the shoulders, and a sharp, 

 raised, ridge-like line, like a second keel, round the edge of the whorls, at a little 

 distance from the suture ; these keels give to the spire a screw-like appearance ; in 

 the early whorls the keel on the shoulders is transversely denticulated. The posterior 

 margins, which slope but slightly backwards, are wide, covering the preceding whorl up 

 to the shoulder, and are very obscurely channelled, almost straight ; the last whorl 

 is short, convex, and produced in front into a wide and somewhat indistinct canal, 

 deeply notched at the extremity. The concentric lines over the margins are rather 



