GASTEROPODA. 165 



margin docs not appear to have been periodically thickened, so that the longi> 

 tudinal costee, 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 costse are all equally prominent, and decussated by the thickened 

 margin ; in others, these costse appear to alternate, one large and one small. In 

 this variety there are from three to five strise or costulge between the more elevated 

 ribs, which are also rounded and smooth. In the common variety the costae 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. Emakginula crassa. /. Soto. Tab. XVIII, fig. 2, a — e. 



Emarginula crassa. J. Sow. 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. 



E. Testa conicd, depressd, vel convexd, costatd ; costis tenuibus, radiantibus, crebris; 

 striis trartsversis granulosis deciissatis ; aperturd ovatd ; margine crenulatd; rimd valde 

 excavatd. 



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. 



LocalUg. 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. The 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. 



