276 EOCENE MOLLUSCA. 
anfractibus convexiusculis, in medio obtuse carinatis ; . postice sub-concavis ; lineis concen- 
tricis ewilissimis, confertis, regularibus, lineis .incrementi perspicuis decussatis: apertura 
ovato-oblongda, antice in canali longo exeunti; labro aleforme, ad carinam sinuato ; sinu 
angusto, profundo, trigono, 
Shell oblong, sub-turreted, having the whole surface ornamented with concentric 
raised lines ; the whorls, seven or eight exclusive of the pullus, are slightly convex, 
and bear on the shoulders an elevated widish-keel, rounded on the upper surface; the 
posterior margins are wide and slightly concave ; and the last whorl, which is rather 
suddenly contracted in front, terminates in a moderately long, rather wide, and nearly 
straight canal. The concentric lines are slender, resembling very fine threads ; regular, 
closely set, and decussated by the prominent lines of growth over the middle and front 
parts of the whorls ; they are more distant and cancellated by the successive reflected 
margins of the sinus over the posterior margins. The aperture is of an oblong-oval 
form; the outer lip much arched, nearly semicircular, but projecting a little towards 
the front, thin and sharp at the edge, and smooth within; the sinus is placed on the 
shoulder, and is rather narrow, deep, and somewhat triangular in shape. 
The ornamentation of the English shells varies from that of the Belgian specimens ; 
in the former, the concentric lines are remarkably slender, crowded over the middle 
and front parts of the whorls, and more distant on the margins ; in the foreign shells, 
on the other hand, they are thick and strong, and are distant over the middle of the 
whorls and crowded over the margins. The lines of growth in the English shells 
appear to be more prominent than in the Belgian specimens, and the concentric lines 
are therefore strongly decussated in the former, while in the latter they are described 
by M. de Koninck as sub-clathratis. In our specimens also, the successive lips of 
the sinus are very prominent, and the concentric lines over the margins are strongly 
decussated. In determining the identity of this shell, the distance in time must be 
taken into consideration, the Belgian shells belonging to the newer Eocene, and the 
English to the older Eocene ; and notwithstanding the differences indicated, I believe 
that both are correctly referable to the same species. 
The specific name, striafula, imposed by M. de Koninck had been previously applied 
by Dujardin to a Miocene Pleurotoma from Mantelin, and the name Waterkeynii 
substituted for it by M. Nyst, must therefore be adopted. 
M. de Koninck describes the species as very rare in Belgium; it appears to be 
equally so in England. 
Size.—Axis, 11-12ths of an inch nearly (23 millim.); diameter, 4-12ths of an 
inch nearly (8 millim.) 
Localities.—Potter’s Bar. Belgian : Basele, Anvers (fide De Kon.), Kleyn-Spauwen 
(fide Myst). 
