246 Dr.T. Wright on the Cidarida? of the Oolites. 



which are not united at their summits. Teeth channelled, not 

 carinated on their internal surface. This genus admits of a na- 

 tural division into two types; in the one the tubercles are 

 smooth, in the other they are crenulated at their base. 



The first type. — Tubercles with the base not crenulated. Are 

 found in our present seas, and fossil in the carboniferous, triasic, 

 cretaceous, and tertiary rocks. They are not found in the Oolitic 

 strata, to which group the present paper is restricted. 



The second type. — Tubercles with the base crenulated. Com- 

 prehends oolitic and triasic forms. 



The circular mouth without indentations serves to distinguish 

 the genus Cidaris from the genus Hemicidaris. The form of 

 the ambulacral arese, the number and arrangement of the gra- 

 nules on the same, the size of the tubercles, and the number of 

 their crenulations afford good specific characters. The ovarial and 

 ocular plates are seldom preserved. The lantern and teeth ought 

 to be carefully studied, as they are sometimes found detached ; 

 the spines likewise yield good specific characters, but they are 

 seldom preserved along with the test. 



Cidaris Fowleri, Wright, n. sp. PI. XL fig. 5 a, b, c. 



Test spheroidal, depressed at both poles ; ambulacral area? flat, 

 narrow and undulated, furnished with two rows of small, re- 

 gular marginal granules and two rows of central blunt irregular 

 microscopic granules ; poriferous avenues wide ; pores oblong 

 and distant ; interambulacral areas furnished with two rows of 

 from 8-10 principal tubercles ; intertubercular spaces wide and 

 covered with small granulations ; spines large, with irregular 

 forward- directed prickles. 



Height 1 inch yoth, transverse diameter 1 inch and y^ths. 

 Specimens from the upper stages of the Oolites measure in 

 height 1 inch and T 8 Qths, transverse diameter 2 inches and y^ths. 



Description. — This beautiful Urchin has been catalogued as 

 C. coronata, but it presents characters very distinct from that 

 form ; a fact which has been ascertained by comparing C. Fowleri 

 with the typical specimens of C. coronata in the British Museum : 

 the latter species has hitherto been found only in France, Germany, 

 and Switzerland, and figured in the works of Goldfuss, Agassiz, 

 and Cotteau. In the Swiss Jura C. coronata characterizes the 

 terrain k chailles, a local formation, the greatest similarity to 

 which exists palseontologically with the lower calcareous grit of 

 Yorkshire ; in l'Albe Wurtembergeoise it appertains to the Coral- 

 line Oolite. 



The ambulacral arese of C. Fowleri arc slightly serpentine and 



