254 Dr. T. Wright on the Cidaridse of the Oolites. 



two convex smooth bands ; another smaller crenulated band sur- 

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

 ments 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. a'enularis 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 Echinidse 

 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 arese 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 Kag 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 species. 



Hemicidaris icaunensis, Cotteau. 



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

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



Test hemispherical, inflated and slightly depressed ; ambulacral 

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

 or four pairs of larger tubercles at the base ; interambulacral 

 arese with two ranges of primary tubercles ; mouth large and 

 decagonal ; margin deeply notched. 



Height y'o^hs of an inch, transverse diameter 1 inch and y^^ths. 

 Desa'iption. — This species is hemispherical and inflated at the 



* Historia Animalium Anglise, t. 7- fig- 21, 1678. 

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



