﻿PROSOBRANCHIATA. 



299 



No. 223. Pleurotoma rotella. F. U. Edwards. Tab. XXXI, fig. 4, a, b. 



P. testa turritd, longitudinaliter arcuato-costellatd, undique transversim sulcata : spird 

 elatd, acuminata : anfractibus sub rectis, ad humeros angulatis ; postice concavis, granulato- 

 marginatis ; ultimo anfractu antice repente coarctato, sub-angulato, incanalem br event, latius- 

 culum, emarginatum, producto ; costellis distantibus, angustis, ad basin tendentibus, sape 

 bifurcatis, postice sub-tuberculosis ; sulcis transversis supra margines posticas et humeros 

 confertis, angustis ; cceterum latioribus, distantioribus : aperturd obovatd ; labro arcuato ; 

 sinu lato, prof undo, sub-semicirculari, ad humerum collocato. 



A rather wide, turreted shell, longitudinally ribbed, and concentrically furrowed : 

 the spire is pointed, much elevated, being nearly twice the length of the aperture, and 

 formed of four or five volutions, exclusive of a smooth, lengthened, sub-cylindrical pullus. 

 The whorls are nearly straight-sided, and angulated at the shoulders ; the posterior 

 margins narrow, concave, and slightly thickened round the suture, where they present 

 a series of small, rounded, rather distant tubercles ; the last whorl is suddenly con- 

 tracted, so as to become obtusely angulated towards the front, and it terminates in a 

 short, but distinct, and moderately wide canal, the anterior extremity of which is 

 notched. The costelhe are rather distant, curved and narrow, and are swelled on the 

 shoulders into small, oblong tubercles ; thence they taper gradually, becoming sharp 

 and elevated lines, not unfrequently furcated, towards the front, and they extend to 

 the very base of the whorl ; the concentric furrows are narrow, shallow, close-set, and 

 regular over the posterior margins and shoulders, but are wider, deeper, and more 

 distant over the middle and front of the whorls. The aperture is nearly oval ; the 

 outer lip thin, sharp-edged, and arched ; and the sinus, which is on the shoulder, is 

 wide, moderately deep, and rounded at the extremity. 



This species presents some analogy with two Pleurotoma? from Cuise Lamotte, at 

 present undescribed, but which have been named respectively P. plicatella and P. 

 normalis by M. Deshayes, to whom I am indebted for specimens ; in the first of these 

 species, however, the shell is more slender, the spire more conical and pointed, the 

 whorls more regularly convex, the posterior margins not so deeply channeled, the 

 anterior canal longer, and the sinus wider and more trigonal ; and in P. normalis the 

 shell is wider, the spire more conical, the posterior margins of the whorls deeper 

 and simple on the sutural edge, the costse more distant and shorter, and the canal 

 longer ; the transverse ornamentation also consists of very slender, closely set, raised 

 lines, and the sinus is placed in the margin. 



Size. — Axis, 5-l2ths of an inch ; diameter, 2 - 5-12ths of an inch. 



Localities. — HighclifF, where it is not uncommon, and Barton, where it appears to 

 be very rare. 



