﻿PROSOBRANCHIATA. 



249 



Calcaire grossier, and may be regarded by some, perhaps not unreasonably, as 

 specifically distinct rather than as constituting a local variety. Thus, in the French 

 shells, the posterior margins of the whorls are so feebly lined that to the naked eye 

 they appear to be smooth < the ribs are more numerous, narrower, and less prominent ; 

 the concentric lines are rather more crowded and more feeble, becoming nearly 

 obsolete ; and the shells themselves are thinner. It appears to me, however, that 

 these variations can scarcely be regarded as of specific value ; while in the relative 

 proportions, the general character of the ornamentation, the condition of the outer lip, 

 particularly the characteristic callus, and the shape and position of the sinus, the 

 French and English shells correspond. On the whole, therefore, I am inclined to 

 regard the English shells as forming merely a coarse, strongly marked variety of the 

 French species. 



The shells from Dax and Bordeaux, referred to this species by Basterot and 

 Grateloup, appear to be distinct, and Desmoulins has separated them under the name 

 P. variabilis. According to Bronn, they correspond with certain Pleurotomoid shells 

 previously separated by Millet as Defranda variabilis. 



Size. — Axis, 8-12ths of an inch (17 millim.); diameter, 3-12ths of an inch 

 (6^ millim.) 



Localities. — Bramshaw, Brook. French: Grignon, Parnes, Mouchy, Courtagnon 

 (fide Desh.), Halaincourt (fide Graves). 



No. 170. Pleurotoma acuticosta. Nj/st.? Tab. XXVIII, fig. 14, a — c. 



Pleukotoma accticosta. Nyst.1 1843. Coq., &c, foss. de Belg., p. 529, No. 454, 



tab. 42, fig. 5. 



— — Morris. 1854. Cat. Brit. Foss., 2d edit., p. 269. 



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

 elevatd, acuminata: anfractibus convexiusculis, postice depressis, sub-canaliculatis ; ultimo 

 anfractu antice coarctato, in canali brevi, indistinclo, latiusculo lerminanti ; costellis 

 obliquis, angmtis, mb-distantibus ; lineis concentricis exilibus, numerosis : aperturd ovatd ; 

 labro leviter arcuato acuto ; sinu lato, sub-semicirculari, in margine collocato. 



Shell oblong, fusiform, longitudinally ribbed, concentrically lined; spire pointed, 

 much produced, nearly equalling three fifths of the entire length of the shell ; whorls, 

 eight or nine, slightly convex ; the posterior margins somewhat depressed and 

 furrowed ; the last whorl contracted in front and forming a wide, short, and indistinct 

 canal. The longitudinal ribs are narrow, rather distant, rounded on the upper 

 surface, and slightly oblique ; the concentric lines very slender, irregular, close-set, 

 becoming obsolete over the posterior margins. The aperture is of an oblong-oval 



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