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 | 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 coste, 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, 4 inch; diameter, rather more than 2-1 2ths of an inch. 
Localities.—Barton. Belgian: Gremittingen (Lower Limburg series). 
No. 17]. Pxievroroma tereticosta. Ff. 2. Hdwards. Tab. XXIX, fig. 5, a—d. 
P. testaé fusiform, sub-turritd, costellata, spiraliter fasciolatd: spird obtusiusculd, 
elevatd, in longitudine aperturam e@quanti: anfractibus depresso-convexis, ad humeros 
sub-angulatis, postice sulco profundo exaratis, marginatis ; ultimo anfractu antice coarctato, 
in canalem brevem latum producto ; costellis numerosis, leviter arcuatis, rotundatis, brevibus; 
Jasciolis spiralibus crebris, irregularibus, alternatim latiusculis et angustioribus ; fasciolis 
anterioribus elevatis, ceteris fere obsoletis: sinu lato, minime profundo, triangulari, in 
margine collocato. 
Var. soror, testa spiraliter sulcata ; canali antico brevior?. 
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 flat-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, 
