﻿PROSOBRANCHIATA. 



315 



which the shoulders are without ornament ; the sides of the whorls in front of the 

 shoulders are very nearly straight ; the posterior margins slope gently backwards, and 

 are very slightly channelled. The sutural edge presents either a single, sharp, ridge-like 

 line, or, more generally, two sharp and very slender, raised lines, separated by a concave 

 furrow ; in the early whorls it is strongly crenulated, but the crenulations afterwards 

 become faint and almost obsolete ; the hollow space between the margin and the 

 shoulder, and the shoulders themselves in the later whorls, are smooth and shining. 

 The concentric bands are depressed, more or less broad in different specimens, and 

 separated by rather deep, concave furrows, which are frequently traversed by a single, 

 very fine, raised line. The last whorl, which is nearly conical, is slightly notched at 

 the base and feebly crested in front. The aperture is narrow, long, and sub-quadrate, 

 and terminates in front in a wide, short, indistinct canal ; the outer lip is moderately 

 arched, thin-edged, and smooth within ; the sinus is wide and deep, with nearly 

 parallel margins, and is placed on the shoulder j and the columella is cylindrical 

 and very slightly twisted. 



This Pleurotoma has a close analogy with P. turbida, for which, in the young- 

 state, it may be mistaken ; but the greater narrowness, and the smooth, shining 

 surface, of the shell, the more conical form as well of the spire as of the body whorl, 

 the unornamented shoulders of the later whorls, and the narrow, subquadrate 

 aperture, sufficiently distinguish it from that species. 



Size. — Axis, 1 inch and 2-12ths, nearly; diameter, rather more than 5-12ths of 

 an inch. 



Locality. — Alum Bay (Stratum No. 29, Prestw.) 



No. 240. Pleurotoma Hantoniensis. F. E. Edwards. Tab. XXXI, fig. 8, a — c. 



Pleurotoma plebeia, var. b. Forbes. 1856. Tert. fluvio-inar. form., &c. (Mem. Geol. 



Surv.), p. 154, t. 5, f. 2. 



P. testa turritd, transversim lineis elevaiis crassis cinctd : spird acuminata : anfractibus 

 depresso-convexis, carina obtusd, nodoso-crenatd, blpartitis; marginibus posticis sub-depressis, 

 excavatis, transversim exilissime lineatis, ad suturam crenulatis ; ultimo anfractu antice valde 

 coarctato, in canalem palulum, ad extremitatem emarginatum, producto ; lineis transversis 

 supra medias partes anfracluum crassis, preeminent 'ibus, sub-distantibus, irregularibus ; inter- 

 stitiis scepe exiliter lineatis : aperturd oblongo-ovali ; labro tenui, simplici, valde arcuato : 

 columella contortd, obscure callosd ; sinu latiusculo, triangularis ad carinam collocato. 



Shell turreted, concentrically and coarsely lined : spire pointed, elevated, a little 

 exceeding the aperture in length. The whorls, eight or nine exclusive of a smooth, 

 conical pullus, are depressedly convex, divided unequally at the shoulder by an obtuse 



