Dr. T. Wright on the Cidarida; of the Oolites. 147 



two convex smooth bands \ another smaller crenulated band sur- 

 rounds the rim of the socket which affords attachment to the liga- 

 iih -nts articulating the spine with the tubercle. The secon- 

 dary spines are small, needle-shaped and compressed, and striated 

 longitudinally. 



Affinities and differences. — This species approaches so near to 

 H. crenularis that it was long regarded as Lamarck's species. 

 The form and development of the spines of the two Urchins how- 

 ever prove them to be distinct; this circumstance shows the 

 necessity of caution in the identification of species of Echinidae 

 in the absence of any of the data upon which a correct opinion can 

 alone be formed* H. intermedia resembles H. icaunensis in its 

 general outline, but is distinguished from that species by its 

 more prominent tubercles, in having the ambulacral areae more 

 undulated and having larger tubercles at the base. These cha- 

 racters likewise sufficiently distinguish it from H. alpina and H. 

 granulosa. 



Locality and stratigraphical range. — One of our specimens was 

 obtained from the spoil of Salperton Tunnel from a bed belong- 

 ing to the Great Oolite ; the other specimen was collected from 

 the Bradford clay near Cirencester. We have never met with H. 

 intermedia in the Inferior Oolite. This Urchin is very abundant 

 in the Coral Rag of Calne, from whence most cabinets have been 

 supplied. The varieties in the Great Oolite are more globular 

 and depressed than those obtained from the Coral Rag. 



History. — As it is uncertain whether we possess H. crenularis 

 in our beds, it is probable that H. intermedia was figured and 

 described by Martin Lister*. Our synonyms show the changes 

 of name through which this species has passed. It has, however, 

 been so accurately described by Prof. Forbes, and so admirably 

 figured t in the ■ Memoirs of the Geological Survey/ that we must 

 refer to that work for further details of the speci* 



Hemicidaris icaunensis, Cotteau. 



Syn. Hemicidaris icaunensis y Cotteau, Echin. Foss. t. 3. fig. 1-5. 

 p. 56 ; Forbes, Geological Survey, Mem. Decade 3. 



Test hemispherical, inflated and slightly depressed ; ambulacral 

 areae with two rows of small marginal tubercles, and with three 

 or four pairs of larger tubercles at the base ; interambulacral 

 areae with two ranges of primary tubercles ; mouth large and 

 decagonal ; margin deeply notched. 



Height T %ths of an inch, transverse diameter 1 inch and y^ths. 

 Description. — This species is hemispherical and inflated at the 



* Historia Animaliura Anglia?, t. 7- fig- -K 1678. 

 t British Organic Remains, Decade 3. pi. 4. 



N 



