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EOCENE MOLLUSCA, 



anfractibus convexiusculis, in medio obtuse carinatis ; postice sub-concavis ; lineis concen- 

 tricis exilissimis, confertis, regularibus, lineis incrementi perspicuis decussaiis : aperturd 

 ovato-oblongd, antice in canali longo exeunti ; labro alaforme, ad carinam sinuato ; sinu 

 angusto, prof undo, 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, striatula, 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, ll-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 Nyst). 



