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EOCENE MOLLUSCA. 



on the edge, and frequently, but not invariably, armed within with three or four 

 pliciform teeth ; the sinus is deep, three-cornered, and placed in the margin. 



A variety occurs in which the shell is slenderer, and the spire more pointed. 



Size. — Axis, 6-12ths of an inch; diameter, rather more than 2-12ths of an inch. 



Localities. — Barton, HighclifF, for the type ; Bramshaw and Alum Bay (Stratum 

 No. 4, Prestwich), for the variety. 



No. 176. Pleurotoma scabriuscula. F. E. Edwards. Tab. XXIX, fig. 2, a — c. 

 Pleurotoma decussata, Lamk. 1 1804. Ann. du Mus., vol. iii, p. 267, No. 25. 



P. testa sub-turritd, tuberculatd, omnino concentrice lineatd : spird obtusiusculd, elatd, 

 in longitudine dimidium totius testa superanti : anfractibus convexis, antice coarctatis, 

 ad humeros sub-angulatis, unicd serie tuberculorum instructis ; marginibus posticis declivis, 

 vix cavatis, granidato-marginafis ; lineis concentricis elevatis, sub-distantibus, simplicibus 

 vel leviter denticulatis : aperturd obovatd, in canali lato, brevi terminatd ; labro arcuato, 

 acuto, intus plicato ; sinu lato, prof undo, sub-trigono, media in margine collocato. 



Far. a, testa tuberculis verticaliter productis, costellas simulantibus. 



Shell turriculated, tuberculated, and ornamented with concentric, raised lines, 

 which cover the whole surface : the spire, consisting of six or seven volutions, is 

 rather thick and elevated, forming a little more than one half of the entire shell. The 

 whorls are convex, slightly contracted in front, and bluntly angulated at the shoulders, 

 where they present a single row of small, oblong tubercles, more or less distant in 

 different individuals, and crossed by the concentric lines, two of which are generally more 

 prominent than the rest ; the posterior margins are moderately wide, gently depressed, 

 very slightly concave, and thickened and granulated round the sutural edge. The 

 concentric lines are prominent, sharp, and not very distant, varying in this respect in 

 different specimens ; they are generally simple and smooth on the edge, but sometimes 

 denticulated by the strongly marked lines of growth. The aperture is of a broadish, 

 oval shape, and terminates anteriorly in a wide and short, but distinct, canal ; the 

 outer lip is much arched, sharp-edged, and plicated within ; the sinus is wide, deep, 

 somewhat triangular in form, and placed in the middle of the margin. 



A variety occurs, rather plentifully, in which the spire is more pointed, and the 

 tubercles on the shoulders of the whorls are lengthened both in front and behind, 

 so as to form short, narrow ribs. 



This shell presents so close a resemblance to P. decussata (Lamk.), that I am 

 reluctant to consider the two as specifically distinct. The French shell is generally 

 narrower, and the body-whorl is less contracted in front and more conical than in the 

 English specimens ; and M. Deshayes describes it as being much shorter than the 

 spire ; but in a series of French specimens, for which I am indebted to the liberality 



