152 CRETACEOUS LAMELLTBRANCHIA. 



Description. — Shell convex, oval, longer than high. Antero-dorsal margin 

 short. Anterior margin produced, somewhat pointed, rounded, curving rapidly to 

 join the slightly convex ventral margin. Posterior margin short, somewhat 

 truncated. Postero-dorsal margin long, convex, with a considerable ventral slope. 

 Umbo prominent, recurved. Lunular region deep. A faint carina extends from 

 the umbo to the postero-ventral extremity. Ornamentation consists of growth- 

 lines. Length 78 mm. Height 70 mm. 



Remarks. — The type, a right valve, now in the British Museum, is the only 

 undoubted example of this species which I have seen. From the nature of the 

 matrix there seems no doubt that this specimen comes from the mammilatum zone. 

 The hinge cannot be made out satisfactorily, but the form of the shell agrees 

 closely with that typical of Isocardia. 



Distribution. — Lower Greensand (zone of Douvilleiceras mammilatum) near 

 Sandgate. 1 



Fam ily— LUCINIDiE, Fleming. 



Genus — Lucina, J. G. Briiguiere, 1797. 

 (' Encyc. Meth., Vers,' pi. eclxxxiv. Lamarck, ' Mum. Soc. Hist. Nat. Paris,' 1799, p. 84.) 



Lucina, sp. Plate XXIV, figs. 2, 3. 



Internal casts of a Lucina have been obtained from the Spilsby Sandstone 

 (zone of Belemnites lateralis) of Donnington and Claxby. A right valve with the 

 shell preserved was found by Mr. Lamplugh in the Spilsby Sandstone at Hoi ton 

 and probably belongs to the same species as the casts. The shell bears numerous 

 small concentric ridges. 



Lucina, sp. Plate XXIV, figs. 4, 5. 



Some internal casts and a portion of an external cast of Lucina have been 



1 Isocardia ? ornata, Forbes, 'Quart. Journ. Geol. Soc.,' vol. i (1845), p. 242, pi. ii, fig. 10, is 

 known only by the imperfect type specimen which is now in the Museum of the Geological Society 

 (No. 2150), and was obtained from the Lower Greensand of Atherfield. It was referred to Opis by 

 d'Orbigny, ' Prodr. de Pal.,' vol. ii (1850), p. 118. 



Isocardia cryptoceras, d'Orbigny, has been recorded by Barrois from the Upper Greensand near 

 Devizes. See ' Terrain Civt. super, do l'Angleterre et de PIrlande ' (1870). p. 01. 



