PROSOBRANCHIATA. 231 
P. testé elongatd, angustd, turritd, acuminatd, longitudinaliter costatd, concentrice 
sulcatd : anfractibus conveviusculis; marginibus posticis angustis, concavis, transversim 
granuloso-lineatis, ad suturam plicatis; sulcis concentricis confertis, antice distantio- 
ribus ; spatis sulcos separantibus lineis incrementi granulatis: apertura oblongo-ovali, 
in canali lato, longiusculo exeunti; labro arcuato; sinu fere semicirculari, in margine 
collocato. 
Var. a.— Testa latiori, breviort. 
Var. B.—Testd laevigata ; sulcis transversis semi-obliteratis. 
Shell elongated, narrow, turreted, pointed, longitudinally ribbed and concentrically 
furrowed; the spire, formed of eight or nine volutions, much produced, equalling in 
length three fifths of the whole shell. . The whorls are slightly convex ; the posterior 
margins narrow, channeled, ornamented with several concentric raised lines, a little 
thickened at the suture, and plicated by the lines of growth of the sinus, which, in 
some specimens, are prominent over the whole margin, granulating the concentric 
lines; the last whorl is rather suddenly contracted in front, and terminates in a wide 
but not very long canal. The furrows in front of the shoulder are close-set, regular 
and equal, but, where the whorl begins to contract, they become more distant and 
irregular: the surface of the intervening spaces is granulated by longitudinal ridges 
formed by the elevated lines of growth; the longitudinal ribs are rather numerous, 
narrow, and extend to the middle of the whorls. The aperture is of a narrow, oblong- 
oval form; the outer lip but slightly arched, and the sinus, which is wide and almost 
semicircular in shape, is placed a little in front of the middle part of the margin. 
Specimens occasionally occur (Var. a, fig. 3 4, c) in which the shell is wider and shorter, 
and the spire is relatively not so much produced; and others, again (Var. [, fig. 3 @), 
in which the ribs disappear as the shell is enlarged, the transverse furrows are shal- 
lower and more closely set, and the lines of growth less prominent, giving to the 
surface a levigated appearance, as if it had been rubbed smooth. 
MM. Nyst and De Koninck have severally described certain shells from Basele, 
Boom, and Kleyn-Spauwen, which they have referred, erroneously in my opinion, to 
the present species. In the general character of the ornamentation these shells 
apparently agree with the English shells; but with them, judging from the figure 
given by Nyst, the spire is relatively longer, the whorls more convex, the posterior 
margins less depressed, giving a more conical and less turreted form to the spire ; the 
body-whorl more suddenly contracted, and the columella more arched: the characters, 
however, which most clearly distinguish the Belgian shells are the form and position of 
the sinus, which is wide and very shallow, and is placed on the shoulder, and not, as 
in the present species, in the margin of the whorls. 
Size.-—Axis, 1 inch and 38-12ths diameter, 4-12ths of an inch. 
