﻿PROSOBRANCHIATA. 



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No. 162. Ple urotoma innexa. Solander. Tab. XXVIII, fig. 1, a — c. 



Mukex innexus. Sol. 1766. Brand. Foss. Hant., p. 19, fig. 30. 



Pleurotoma innexa. Forbes. 1856. Tert. Fluv. Mar. Format., &c. ; Mem. Geol. Surv., 

 p. 154, t. 5, fig. 5. 



P. testa elongato-fusiformi, reticulato-crenulatd : spird sub-conicd, elevatd : anfractibus 

 vix convexis, tineas etevatas concentricas, et costettas longitudinales, sese decussantes, 

 gerentibus ; marginibus posticis angustis, spiraliter sulcatis, ad suturam granulatis ; ultimo 

 anfractu in canali patulo, per-brevi, exeunti ; costellis acutis, usque ad basin tendentibus, 

 arcuatis, tuber culatis : aperturd oblongo-ovali, angustd ; labro aliforme, intus nonnunquam 

 obscure denticulato ; sinu lato, rotundato, in margine collocato ; labio angusto, incrassato. 



Shell elongated, fusiform, and ornamented with concentric and longitudinal raised 

 lines, nearly equally prominent, and which, from their decussation, present the 

 appearance of fine network. The spire is thick, nearly conical, and much elevated, 

 almost equalling two thirds of the entire length of the shell. The whorls, eight or nine, 

 exclusive of a pointed pullus of three volutions, are short, very slightly convex, nearly 

 flat-sided ; the posterior margins are very narrow, and present a more or less shallow 

 transverse furrow ; they are thickened on the edge of the suture, which is bordered 

 by a single row of small, round, or somewhat oblong, granulations. The longitudinal 

 ribs, which are narrow and sharp, extend from the marginal granulations to the very 

 front of the whorl, and are rather strongly curved over the middle ; in general the 

 ribs are a little more prominent than the concentric lines, and are thickened at the 

 points of decussation, like the knots of a net, forming rows of small tubercles, the 

 last of which, immediately in front of the margin, is more prominent than the rest. 

 The concentric lines are irregular, close-set at the base, distant over the front of 

 the whorl, and become more or less crowded as they approach the posterior margin. 

 The aperture is of a narrow, oblong-ovate form, and terminates in a short, wide canal, 

 rather deeply notched in front ; the outer lip is much arched, sharp at the edge, 

 thickened within, and presents three or four thick, tooth-like callosities, of which the 

 posterior one in front of the sinus is large and prominent ; the inner lip is narrow 

 and thickened ; the columella is slightly curved, and bears in front a small crest ; 

 the sinus is rounded and wide, occupying the whole width of the margin. 



The figure of this shell, given by Brander, is not executed with the felicity which 

 usually characterises that author's work, and to this circumstance, probably, is to be 

 attributed the difficulty which the Continental writers have had in identifying the 

 species. Thus Lamarck and, after him, Deshayes, referred P. innexa, although with 

 doubt, to P. undata (Lamk.), from which species, however, it is easily distinguished 



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