﻿PROSOBRANCHIATA. 



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raised lines, so faint as to be scarcely visible to the naked eye ; the longitudinal ribs 

 also are thicker and more distant, and they extend to the very front of the whorl. 



Size. — Axis, rather more than 6-1 2ths of an inch; diameter, rather more than 

 2-12ths of an inch. 



Localities. — Headon Hill, and Colwell Bay, Isle of Wight ; and Hordwell. 



No. 251. Borsonia semicostata. F. E. Edwards. Tab. XXXIII, fig. 13, a, b. 



B. testa ovato-fusiformi, semi-costatd, omnino.spiraliter lineatd: spird elatd, turrild : 

 anfractibus convexiuscidis, postice canaliculatis ; costis numerosis, rotundatis ; lineis spi- 

 ralibus elevatis, aculis, supra margines anfractuum exilibus, regidaribus ; caterum irregu- 

 laribus, sub-distantibus, duabus sub-medianis elatioribus : aperturd oblongo-ovali, in canalem 

 latum perbrevem productd ; labro leviter arcuato, postice sinuato, intus lesvi ; columella 

 oblique inequaliter biplicatd, plica anlicd minori. 



Shell small, ovately fusiform, longitudinally ribbed, and covered with raised, con- 

 centric lines ; the spire turreted and elevated, exceeding the aperture in length. The 

 whorls, which are six in number without the pullus, are convex, and channelled round 

 the posterior margins ; the last whorl is rather suddenly contracted towards the front, 

 tapering thence gradually towards the base, where it terminates in a very short, wide 

 canal. The ribs are rather numerous, not very broad, rounded on the upper surface, 

 of equal thickness, and short, ending abruptly where the whorl contracts ; the trans- 

 verse lines over the posterior margins are yery fine, even, and regular ; a sharp, 

 elevated line crosses the shoulders, in front of which appear four other elevated lines, 

 which gradually become more and more prominent and distant as they recede from 

 the shoulders ; the front two are more prominent and wider apart than the rest ; they 

 are separated by a broad, concave furrow, and swelled into small, tooth-like knobs, 

 where they cross the longitudinal ribs ; the lines over the front part of the whorl and 

 the canal are irregular and very obscure, almost obsolete. The aperture is of an 

 oblong-oval shape ; the outer lip is very slightly arched, and presents a shallow and 

 not very wide, rounded sinus, placed in the marginal depression ; the columella 

 is nearly straight, and furnished with two unequal, oblique folds, placed near the 

 middle, the front one of which is the smaller. 



In general aspect, this shell so closely resembles Borsonia sulcata, that a doubt 

 may fairly be raised whether it ought not to be regarded as a variety of that species. 

 It will be seen, however, on comparison, that in B. sulcata the spire is longer, that 

 the posterior margins are not so wide nor so deeply channelled, and that they are 

 spirally lined, and not smooth ; that the costse are narrower and more numerous, and 

 the transverse ornamentation quite distinct in character ; that the outer lip is not so 



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