BEITISH FOSSILS. 



a 



specimen presented to the Museum of Practical Geology by my 

 friend Mr. C. F. Cockburn of the Eoyal Artillery, who found it 

 in the White Chalk at Dover. 



11. 



CARDIASTER ROSTRATUS. 



Diagnosis. C. testa lateraliter compressd, apice in rostrum elongatum 

 elevatumque producto. 



For some time I was under the impression that this extraordinary 

 and anomalous little urchin of which specimens were kindly com- 

 municated by Mr. Bowerbank, Mr. Wetherell, and Mr. Woodward, 

 was the young of the Cardiaster excentricus, different as its 

 outline is. The series of specimens of various sizes of the latter 

 species shown me by Mr. Rose, (who has also found the kind now 

 figured,) convinces me that it is necessary to regard this beaked 

 and iVeoera-like form of Cardiaster as distinct. All the examples 

 are impressed with the same peculiarities. The number submitted 

 to me has been seven, including fragments ; and in addition to 

 those lent for examination are two fine specimens, one of them nearly 

 entire, foimd by Mr. Cockburn in the Chalk with Flints at Bostal 

 Heath, near Plumstead, and generously presented by that gentleman 

 to the Museum of Practical Geology. 



The striking feature of this form is the rhomboidal profile which 

 it exhibits in consequence of the obliquity of the anteal and posteal 

 truncations, both inclining forwards at considerable angles. The 

 anteal ambulacrpJ sulcus is very deep, long, and narrow ; it rises 

 obliquely to a great height in consequence of the elevation of the 

 apical disk upon a sort of beak. The genital plates are a^ssembled 

 just below its summit, which is notched by the turning over, as 

 it were, of the anteal furrow. The details of the lateral ambulacra, 

 in consequence of their being completely plane and very obscure, 

 can with difficulty be distinguished. The rostrum bends forward 

 slightly in its upper part. The summit of the back is more or less 

 sharply carinated, and declines rapidly with a faint concave curve, 

 until it terminates in the summit of the very oblique and rapidly 

 declining posterior truncation, in the uppermost part of which, 

 at rather less than the total height of the body, is the anus, 

 placed at one end of a groove. The whole of the dorsal surface 

 of the test is covered with granules interspersed with scattered 

 minute tubercles, which become more numerous on the slightly 

 tumid cheeks. The fascicle is strongly and distinctly marked, 



