PROSOBRANCHIATA. 221 



nanti ; striis concentricis confer tis,irregularibus, in marginibus posticis tenuissimis ; ca'teris, 

 striis eminentioribus cum aliis lenuibus alternantibus : aperturd angusto-ovali ; labro 

 arcuato, tenui ; sinu lato, sub-trigono, in margine collocato ; canali subrecto, antice rejlexo, 

 emarginato. 



Shell elongated, fusiform, having the whole surface ornamented with concentric 

 raised lines ; the spire much elevated, being nearly as long as the body-whorl, 

 pointed, and formed of ten or eleven volutions. The whorls are rather convex, sharply 

 angulated at the shoulders, and armed with a row of transversely compressed, tooth- 

 like tubercles, rounded in front, sharp, sometimes almost carinated at the edges, 

 varying both in number and prominence in different individuals, and occasionally 

 having their bases prolonged into short, rounded costellse ; the posterior margins 

 are moderately wide, straight, or but very slightly hollowed out, and a little thickened 

 at the sutural edges, where they are sometimes obliquely plicated by the lines of 

 growth of the sinus ; the surface between the suture and the shoulder is covered with 

 very fine, almost obsolete, concentric lines, two of which, running round the sutural 

 edge, are more elevated than the rest ; the middle and front parts of the whorls are 

 ornamented with numerous, irregular, undulating, thread-like, raised lines ; of these 

 some are prominent, and between them appear two or three others very slender, so 

 much so, in fact, as to be barely perceptible by the naked eye. The aperture is of a 

 narrow, ovate form, and terminates in a long, moderately wide, and nearly straight 

 canal, bent backwards, and notched at the anterior extremity; the outer lip is thin, 

 sharp-edged, and slightly arched ; the sinus wide, rather deep, sub-trigonal in form, 

 and placed in the very middle of the margin ; the anterior extremity of the columella 

 presents a prominent ridge or crest, formed by the notch of the canal. 



This species is very common and widely distributed in the French formations ; in 

 England it is, apparently, confined to the middle beds of the Bracklesham Bay series. 

 Our specimens are narrower than the French type ; and in this respect and in the 

 character of the transverse ornamentation they agree with the variety a of Deshayes ; 

 I have not met with the other variety recorded by that author, nor do our shells 

 appear to have attained the size of those from the French beds. D'Orbigny, 

 (loc. cit.) gives Claiborne, in Alabama (U.S.), as a locality. I cannot but think, 

 however, that this identification is somewhat questionable. The present species is 

 the type of a group of closely analogous forms, and two English species (P. exorta 

 and P. macilenta, Sol.), which, as will be afterwards shown, are perfectly distinct, 

 have in fact been confounded with it. No authority is cited by the author, and 

 I have therefore given Claiborne as a questionable locality. 



Size. — Axis, 1 inch and 7-12ths (40 millim.) ; diameter, not quite 7-12ths of an 

 inch (15 millim., nearly). 



Localities. — Bracklesham Bay ; Bramshaw. French — Grignon, Parnes, Mouchy, 

 Courtagnon, &c, La Chapelle pres Senlis, Valmondois (fide Desk.), Cuise-Lamotte, 



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