﻿250 



EOCENE MOLLUSCA. 



form; the outer lip a little arched, thin, sharp-edged, and smooth within; the sinus 

 wide and nearly semicircular, and placed in the posterior margin. 



The figure of P. acuticosta in M. Nyst's work is, unfortunately, so indistinct that 

 it affords but little assistance towards an identification. The English shell, however, 

 agrees tolerably well with the description given by that author, and I have referred 

 it to M. Nyst's species, although with hesitation, as I have not had an opportunity 

 of comparing it with any Belgian specimen. 



The English shells which the present Pleurotoma most nearly resembles, are 

 those referred to P. plicata (Lamk.) ; but this species differs from them in the more 

 slender form of the shell, the more depressed margins of the whorls, the narrower, 

 more numerous, and more regular costas, and the finer transverse lineation ; and, in the 

 specimen I possess, the outer lip is not thickened within, nor does it present the callus 

 which characterises P. plicata. 



The species appears to be very rare. 



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

 Localities. — Barton. Belgian: Gremittingen (Lower Limburg series). 



No. 171. Pleurotoma tereticosta. F. E. Edwards. Tab. XXIX, fig. 5, a — d. 



P. testa fusiformi, sub-turritd, costellatd, spiraliter fasciolatd: spird obtusiusculd, 

 elevatd, in longitudine aperturam aquanti : anfractibus depresso-convewis, ad humeros 

 sub-angulatis, postice sulco prof undo exaratis,marginatis ; ultimo anfractu antice coarctato, 

 in canalem brevem latum producto ; costellis numerosis, leviter arcuatis, rotundatis, brevibus; 

 fasciolis spiralibus crebris, irregularibus, alternatim latiusculis et angustioribus ; fasciolis 

 anterioribus elevatis, cateris fere obsoletis : sinu lato, minime prof undo, triangulari, in 

 margine collocato. 



Var. soror, testa spiraliter sulcata; canali antico breviori. 



Shell fusiform, longitudinally ribbed, and spirally girt with ribbon-like bands : 

 the spire is thickish and moderately elevated, not exceeding the aperture in length : 

 the whorls, five or six in number without the pullus, are rather fiat-sided and bluntly 

 angulated at the shoulders ; the posterior margins narrow, deeply furrowed, and 

 much thickened at the edges, where they present a moderately wide band running 

 round the suture. The longitudinal ribs are numerous (twelve to fourteen), slightly 

 curved, round and smooth on the upper surface, short, not extending beyond the 

 middle of the whorl, tapering towards the front, and occasionally bifurcated ; the 

 posterior extremities are continued over the shoulder up to the sutural band ; the 

 spiral bands are numerous and irregular, ribbon-like bands alternating with other 

 narrower bands ; over the anterior canal and the front part of the whorl up to 

 the termination of the ribs, these bands are elevated and distinct; elsewhere they 

 are nearly obsolete. The body-whorl contracts rather suddenly about the middle, 



