GASTEROPODA. 165 



not appear to have been periodically thickened, so that the longitudinal costae, which 

 are 20 — 22, stand prominently out, and the shell appears striated with small punctures 

 between them ; these small holes are probably the alveoli left by the decussating 

 margin. In most of the specimens of the more common variety the costae are all 

 equally prominent, and decussated by the thickened margin ; in others, these costae 

 appear to alternate, one large and one small. In this variety there are from three 

 to five striae or costulse between the more elevated ribs, which are also rounded 

 and smooth. In the common variety the costas are made rough and nodulous by the 

 thickened margin of the shell. 



Specimens of this species are occasionally loaded with a mass of cellepora. 



In some specimens the rays are all equally prominent, amounting to upwards of 

 sixty, but in the greater number there is a smaller intermediate one. 



2. Emarginula crassa. /. Soio. Tab. XVIII, fig. 2, a — e. 



Emarginula crassa. J. Soiv. Min. Conch, t. 33, 1813. 



— Nyst. Coq. foss. de Belg. p. 352, pi. 36, fig. 3, 1844. 



— Forbes. An. and Mag. Nat. Hist. vol. xiv, p. 410, pi. 10, fig. 1, 1844. 



F. Testa conicd, depressd, vel convexd, costatd ; costis tenuibus, radiantilus, crehris ; 

 striis transversis granulosis decussaiis ; aperturd ovatd ; margine crenulatd; rimd valde 

 excavafd. 



Shell depressedly conical and striated, with the anterior dorsal portion convex ; 

 longitudinally striated and transversely decussated ; base ovate ; margin crenulated ; 

 fissure large and deep. 



Longitudinal diameter, 2 inches. 



Locality. Cor. Crag, Sutton and Ramsholt. 



Red Crag, Sutton and Newbourn. Recent, British Seas. 



I have only a few specimens of this shell from either formation. According to 

 Professor E. Forbes, the species is found living in the Scandinavian seas, and has 

 recently been dredged up alive by Mr. M'Andrew off the Scottish coast. The 

 fissure is rather wide, and in depth about one fifth of the entire length of the anterior 

 portion, and the breadth of the base is less before than it is behind the vertex, which 

 is itself variable in position, as may be seen in the figures above referred to. Tlie 

 longest diameter of my largest specimen measures two inches, and is from the Red 

 Crag, at Newbourn ; but a larger individual has, I am informed, been obtained by 

 W. H. Alexander, Esq. of Ipswich. 



Figs, c and e are from the Coralline Crag, Ramsholt. 



