PROM THE WHITE CHALK. 



339 



Dr. 



Barrois' General Classification. 



Mr. C. Evans' Classification in East Surrey and 

 West Kent. 



Zone 



a Belemnitella. 



Grravesend Beds ? 





Marsujntes. 



M. cor-angninum. 



M. cor-testudinarium. 



Charlton and Croydon Beds. 

 Riddlesdown Beds. 





Holaster planus. 



Kenley Beds. 





Terebratulina gracilis. 



Whiteleaf Beds. 





Inoceranms lahiatus. 



Upper Marden-Park Beds. 





Belemnites j^letius. 



Lower Marden-Park Beds. 





Holaster suh-glohosus. 



Oxtead Beds. 



Zone 



a Pecf.en asper. 

 Ammonites inflatus. 





MiCRASTER BREVIS, DesoT. PI. LXXV, figs. 2 </, 3 a—g. 



MiCRASTER LATUS, Sismonda. Echin. foss. de Nizza, p. 29, tab. i, fig. 13, 1843. 



— BREVIS Hebert. Etud. sur les terr. Cretace's ; Mem. Soc. Geol. de 



France, 2e ser., torn, v, tab. xxix, fig. 19, 1854. 

 Spatangus ananchytoides, De5»zoi<^. Tabl. Synom., p. 406, 1837. 

 MiCRASTER BREVIS, Desor. Synopsis des Echinides Foss., p. 364, 1858. 



Diagnosis. — Test cordiform, very short, as broad as it is long ; antero-lateral ambulacra 

 long and wide, postero-lateral pair shorter ; poriferous zones wide, holes forming a pair 

 placed far apart. Test elevated, sometimes conoidal ; anteal sulcus very shallow ; single 

 ambulacrum similar in structure to the anterior pair ; posterior border narrow and very 

 obliquely truncated. 



Description. — This Urchin appears to belong to the " Craie a /lippurites " and has 

 ixany stmctural affinities with certain forms of 31. cor-testudinarium ; it is, however, a 

 much wider shell with a more elevated upper surface, and as far as external form goes 

 very different from that species ; the summit is excentral, a little nearer the anterior 

 border. The ambulacral areas are built of narrow elongated plates, and the pores 

 forming a pair are placed wider apart than m any of the congeneric forms I have 

 described. 



My late friend, Monsieur Michelin, sent me several very good type shells from the 

 " Craie a /lippurites " from Sougraigne, near les Bains de Rennes, and Soulage, Cor- 

 bieres, Aude ; it is found also at Tuco, near CaseneuvCj " Craie de Tercis au Perigord 



