PROSOBRANCHIATA. 247 
the spire. The aperture is of an oblong-ovate form, and terminates anteriorly in 
a short, but distinct and moderately wide, canal ; the outer lip is very slightly arched, 
nearly straight, sharp-edged, and presents within, near the posterior extremity, 
and immediately under the shoulder, a single large, tooth-shaped callosity ; the inner 
lip is very narrow, barely extending to the front of the columella; the sinus is nearly 
triangular in form, deep and wide, extending across the whole of the posterior 
margin. 
Size—Axis, 3°4-12ths of an inch; diameter, 1°75-12ths of an inch. 
Localities —Highcliff, where it is not uncommon; Haverstock Hill. 
No. 168. Pievrotoma compnuowsEa. J. &. Fdwards. Tab. XXVIII, fig. 13, a—/. 
P. testd angustd, elongata, sub-turritd, longitudinaliter costatd, concentrice lineata : 
spird acuminata, elevaté: anfractibus depresso-convexis, ad humeros sub-angulatis ; 
marginibus posticis latiusculis, concavis, ad suturam distanter granulatis ; ultimo anfractu 
brevi, antice coarctato; costellis curvis, brevibus, plus minusve numerosis; lineis con- 
centricis, supra margines fere obsoletis, caeterum elevatis, acutis, sepe denticulatis : 
apertura oblongo-ovali, in canali brevi, sub-recto exeunti; labro sub-aliformi, acuto, sinu 
Jato, minime profundo, in margine collocato. 
Var. avira, testa anfractibus unica serie tuberculorum coronatis. 
A long, narrow, turriculate shell, ribbed, and concentrically lined: the spire, 
which forms two thirds of the whole shell, consists of seven or eight volutions : 
the whorls are flatly convex on the sides, angulated at the shoulders, contracting 
rather suddenly in front, and having the posterior margins widely channelled and 
bordered on the sutural edge by a single row of round, rather distant granules, 
corresponding with the ribs, and variable in size; the angulated shoulders and 
channelled margins give a turriculate character to the spire. The longitudinal ribs are 
more or less numerous in different specimens; they are curved, sharp, and terminate 
abruptly where the whorl contracts ; the concentric lines over the posterior margins 
are close-set, and so fine as to be barely visible to the naked eye; over the middle 
and front parts of the whorl they are moderately distant, elevated, sharp, and generally 
denticulated where they cross the ribs. The aperture is of an oblong-oval shape, and 
terminates in a wide, short, but distinct and nearly straight canal; the outer lip is 
expanded anteriorly, sharp-edged, and smooth within; and the sinus, which is wide, 
rather shallow, and rounded, is placed in the margin. 
I possess specimens both from Clarendon and Southampton, in which the ribs are 
wanting, and the whorls are girt round the shoulders with a single row of knob-like 
tubercles ; in all other respects these shells agree with the typical P. gomphoidea, 
of which, therefore, I consider them to be a variety. 
