4 



BRITISH FOSSILS. 



the body. They are minutely and closely striated throughout their 

 length, but the striae are rather broader than the raised interstices. 

 The base of each spine has a narrow elevated fold surrounding it above 

 its ring of crenulations, which are numerous^ oblong, and closely and 

 regularly set. The secondary spines (those surrounding the primaries 

 on the interambulacral areas and entirely occupying the ambula- 

 oral spaces) are very small, compressed, rather spatulate and longitu- 

 dinally striated. One of the largest measured two-tenths of an inch 

 in length. I have seen traces of pedicellarise, but not sufficiently 

 perfect for description. 



Locality and Geological Position. — This species is very abundant, and 

 found in a beautiful state of preservation in the Coral Rag of Calne. 

 It is scarcer near Weymouth. It occurs also in the same stratum at 

 Malton, and is recorded from the Coral Rag of Yorkshire by Professor 

 Phillips. Mr. Buckman has figured a remarkably fine specimen from 

 the neighbourhood of Cheltenham. In consequence of the doubts 

 hanging over the identification of the British with the foreign Hemici- 

 daris crenularis, I do not venture to give its foreign distribution. 



Explanation of the Plate. 



Fig. 1 . Middle-sized specimen of the sub-depressed form of Hemicidaris intermedia seen 

 in profile ; an outline of the tall variety, from a specimen in the British Museum, is drawn 

 around it. 



Fig. 2. Dorsal surface ; and Fig. 3, ventral surface of the same specimen. 

 Fig. 4. Ambulacral and interambulacral plates and their sculpture, taken from the 

 centre of the sides. 



Fig. 5. Ambulacral and interambulacral plates of the neighbourhood of the mouth. 

 Fig. 6. A single primary tubercle. 

 Fig. 7. Genital and ocular disk. 



Fig. 8. Spines from a specimen presented to the Geological Survey by Mr. Clark of 

 Sandgate. 



Fig. 9. Base of a primary spine magnified. 

 Figs. 10 and 11. Small secondary spines. 

 Figs. 4 — 7 and 9 — 1 1 are magnified. 



Edward Forbes. 



June, 1850. 



