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EOCENE MOLLUSCA. 



whorl, and are much shortened on the earlier whorls, assuming the appearance of 

 oblong tubercles ; and the decussation by the concentric lines disappears. 



The present species presents a close analogy with P. scabriuscula, with which 

 it may, especially in the young state, be readily confounded. On comparing adult 

 shells, however, it will be found that, in this species, the shell is wider, the spire 

 more pointed, the whorls less bluntly angulated at the shoulders, and more 

 depressed and more deeply channeled round the margin, giving a decidedly turreted 

 character to the spire ; the whorls themselves are more numerous and shorter, 

 and, in the typical form, the sharp ribs and prominent concentric lines give a rougher 

 aspect to the surface. In the varieties a somewhat closer approximation will be 

 found in the ornamentation of the two species ; but, in other respects, the charac- 

 teristic distinctions are preserved. 



From P. constricta, the only other species with which it might be confounded, 

 it is separated by the depressed margins, and more sharply angulated shoulders 

 of the whorls, the more regular costellation, and the deep, narrow sinus of that species. 



Size. — Axis, rather more than 8-12ths of an inch ; diameter, 3-12ths of an inch. 



Localities. — Barton, HighclifF; not common. 



No. 178. Pleurotoma constricta. F. E. Edwards. Tab. XXIX, fig. 1, a — c. 



P. testa elongato-fusiforwi, longitudinaliter costellatd, concentrice lineatd : spird 

 conoided, sub-acuminatd, aperturam in longitudine paullo superanti : anfractibus depresso- 

 convexis, ultimo anfractu in canali brevi, lerminanti ; marginibus posticis leviter declivis, 

 canaliculatis, plicatis, ad suturam marginatis ; costellis crebris, angustis, obliquis ; lineis 

 concentricis, acutis, denticulatis : aperturd oblong o-ovali ; labro leviter arcuato ; sinu 

 angusto, prof undo, trigono, untied in margine collocato. 



Shell elongated, fusiform, longitudinally ribbed, and concentrically lined; the 

 spire, formed of seven or eight whorls, is rather conical, pointed, and moderately 

 elevated, barely exceeding the body-whorl in length ; whorls flatly convex ; the 

 posterior margins widely and deeply channeled, thickened at the sutural edges, and 

 bordered by a single sharp, prominently raised line ; the surface of the marginal 

 furrow presents a series of prominent, curved plications, formed by the successive 

 margins of the advancing sinus. The longitudinal ribs are numerous, slender, 

 oblique, slightl)< curved, and extend almost to the very front of the whorl; the 

 concentric lines are sharp, prominent, more or less distant in different individuals, 

 and denticulated at the points where they cross the ribs. The aperture is of an 

 oblong-oval form, and terminates in front in a short, moderately wide, canal ; the 

 outer lip is but slightly arched, thin, sharp-edged, and smooth within; the sinus 

 is trigonal, narrow, very deep, and placed in the front part of the margin. 



