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; 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. Prevroroma Hantoniensis. Ff. 2. Edwards. Tab. XXXI, fig. 8, a—e. 
PLEUROTOMA PLEBEIA, var. 6. Forbes. 1856. Tert. fluvio-mar. form., &c. (Mem. Geol. 
Surv.) po54, t.-5, f5 2: 
P. testa turritd, transversim lines elevatis crassis cinctd : spird acuminata : anfractibus 
depresso-conveais, carind obtusa, nodoso-crenatd, bipartitis; marginibus posticis sub-depressis, 
excavatis, transversim exilissime lineatis, ad suturam crenulatis ; ultimo anfractu antice valde 
coarctato, in canalem patulum, ad eatremitatem emarginatum, producto ; lineis trunsversis 
supra medias partes anfractuum crassis, preeminentibus, sub-distantibus, irregularibus; tinter- 
stitiis sepe ewiliter lineatis: apertura oblongo-ovali ; labro tenui, simplici, valde arcuato : 
columella contortd, obscure callosd ; sinu latiusculo, triangulari, 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 
