﻿PROSOBRANCHIATA. 



307 



and regular on the posterior margins and shoulders ; over the middle of the whorls 

 four or five thicker and coarser lines appear, between which finer lines intervene ; and 

 over the front of the last whorl and the canal the lines again become close-set, equal, 

 and regular ; the whole are roughened, those over the margins almost decussated, by 

 the lines of growth. The aperture is subquadrate, and terminates in a short, mode- 

 rately wide, and nearly straight canal ; the outer lip is very slightly arched, almost 

 straight ; and the sinus, which is very wide, shallow, and pointed at the extremity, is 

 placed on the shoulder. 



The transverse lineation, associated with the acutely angular whorls and the wide, 

 pointed sinus, distinguish this Pleurotoma from all its congeners ; the species is appa- 

 rently very rare. 



Size. — Axis, rather more than 9-12ths of an inch ; diameter, 3-12ths of an inch. 

 Locality. — Bracklesham Bay. 



No. 233. Pleurotoma rotundata. F. E. Edwards. Tab. XXXI, fig. 9, a, b. 



P. testa oblongo-fusiformi, turritd, omnino spiraliter exilissime lineatd ; anfractibus 

 depresso-convexis, ad humeros rotundatis vel obtuse angulatis, in juventd arcuato-crenulatis, 

 deinde inermibus ; postice sub-depressis, concavis, plicato-marginatis ; ultimo anfractu in 

 canalem longiuscidum angustum producto ; lineis spiralibus conferiis, exilibus, incequalibus, 

 irregularibus : aperturd oblongo-ovali ; lubro leviter arcuato, ad humerum sinuato ; sinu 

 latiusculo, mediocriter prof undo, sub-semi-elliptico. 



An oblong, fusiform, turreted shell, covered with very fine transverse lines ; the 

 spire is somewhat cylindrical, pointed, and produced, nearly equalling the aperture in 

 length. The whorls, six or seven, are depressedly convex, and rounded at the 

 shoulders, which in the young state present a close-set series of narrow, crescent- 

 shaped plications, but which afterwards become round and simple, or occasionally are 

 girt with a very narrow and slightly elevated, keel-like band, imparting an obscurely 

 angulated appearance to the shoulder ; the posterior margins are slightly depressed, 

 deeply concave, and bordered round the suture by a prominent band, formed of two or 

 three undulating, raised lines, finely plicated ; the last whorl is much contracted about 

 the middle, whence it tapers gradually towards the base, forming a moderately long 

 and rather narrow canal. The spiral lines are very fine, even, and close-set over the 

 posterior margins and shoulders of the whorls ; over the middle and front parts they 

 are more distant and irregular, broader and somewhat depressed lines alternating with 

 exceedingly slender lines ; and all are more or less feebly granulated by the lines of 

 growth. The aperture is of an oblong-oval shape ; the outer lip moderately arched, 

 and the sinus, which is placed on the shoulder, is rather wide, not very deep, rounded 

 at the extremity, and of a nearly semi-elliptical shape. 



