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EOCENE MOLLUSCA. 



tioned species P. comma certainly presents a general resemblance, but is separable from 

 it by the short curved costellse, which ornament the shoulders, instead of the quadrate 

 tubercles which distinguish P. denticula. The English species most closely resembling 

 P. comma is P. obscurata, a species which may be reasonably expected to occur in 

 the nearly synchronous deposit at Stubbington, and in which the narrow, oblong, 

 compressed tubercles approach very nearly in character to the short costellse of 

 P. comma ; the principal distinction appears to be in the condition of the middle of 

 the volutions, which in P. obscurata are transversely lined instead of being smooth as 

 in P. comma ; but, although this difference does not appear to be of much value, I have 

 not ventured, in the absence of any specimen of P. comma for comparison, to regard 

 the two species as identical. 

 Locality. — Stubbington. 



No. 207. Pleurotoma Prestwichii. F. E. Edwards. Tab. XXX, fig. 3, a — d. 



P. testa elongatd, sub-fusiformi, longitudinaliter costatd ; spiraliter lineatd: spird 

 elevatd acuminata: anfractibus rotundato-convexis ; costellis numerosis, curvis ; lineis 

 spiralibus confertis, irregularibus, supra partes medias anfractuum obsoletis ; cceteris 

 perspicuis : aperturd oblongo-ovali ; labro arcuato, acuto ; sinu ad humeritm collocato, lato, 

 prof undo, sub-trigono. 



Far. : testa anfractibus convexiusculis, ad humeros angulatis, antice sub-conicis. 



Shell lengthened, fusiform, longitudinally ribbed, spirally lined : the spire pointed, 

 elevated, rather exceeding the aperture in length : the whorls, eight or nine, roundedly 

 convex, a little thickened round the suture, and very generally bordered by two or 

 three raised lines ; the last whorl is much contracted in front and produced into a 

 long, open, narrow canal. The longitudinal ribs are numerous, varying in number in 

 different specimens, rounded, curved, scarcely extending in front to the middle of the 

 whorls, but continued backwards to the very suture ; the concentric lines close set 

 and irregular, almost obsolete over the middle of the whorls, but elsewhere prominent 

 and well defined ; for the most part they are thick and rounded, but frequently 

 smaller thread-like lines intervene. The aperture is of an oblong-oval shape ; the 

 outer lip much arched, projecting at the middle, thin and sharp on the edge, 

 smooth within ; and the sinus, which is placed on the shoulder, very wide, rather 

 deep, and triangular in form. 



A variety occurs plentifully in which the whorls are less convex on the sides, 

 giving a subconical character to the spire, and are bluntly angulated at the shoulder ; 

 and the front part of the last whorl is not so much contracted as in the type. 



Size. — Axis, 1 inch and 4-12ths ; diameter, rather more than 5-12ths of an inch. 



Localities. — Clarendon, where both forms are abundant, and Alum Bay (Stratum 

 No. 4, Prestwich). 



