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



portionately large nor are the basal tubercles so numerous as 

 those delineated in Agassiz's figure. We consider our Urchin, 

 however, merely as a variety of the Swiss species, for which we 

 propose the name var. granulans. This beautiful species is 

 easily distinguished from its congeners by the structure of the 

 ambulacra! arese, which are convex, prominent, and thickly 

 covered with small close-set granulations unlike any other species 

 of Hemicidaris yet known. 



Locality and stratigraphical range. — This species was collected 

 from the Bradford clay of Pickwick, Wilts ; a valve of Ter. digona 

 was attached to the test, and it is adherent to Ter. concinna. 

 Plates of this Urchin have been found in the same stratum at the 

 Tetbury Road Station of the Great Western Railway. Mr. Lowe 

 of Chippenham has found it in the Forest marble of Wilts, but 

 it is a rare species. 



History. — First figured and described by Agassiz in the ' De- 

 scription des Echinodermes Fossiles de la Suisse/ afterwards iden- 

 tified in the British Museum collection by Mr. S. P. Woodward, 

 and recorded by Prof. Forbes in Decade 3. of his ' Memoirs of 

 the Geological Survey/ and now described as a British species for 

 the first time. 



Hemicidaris granulosa, Wright. PI. IV. fig. 4 a, b, c. 



Test spheroidal, depressed ; ambulacral arese straight, with two 

 rows of prominent defined granules, the three inferior pair 

 only being perforated and raised upon crenulated mammillary 

 eminences ; interambulacral arese with from two to three pairs 

 of primary tubercles, the superior part of the arese being 

 occupied with warty granules ; apical rosette formed of large 

 petaloidal plates. 



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



Description. — This beautiful Urchin constitutes a well-marked 

 species ; the double row of prominent wart-like granules on the 

 ambulacral arese, which are neither perforated nor raised on 

 eminences, serving as a good diagnostic character. The base of 

 the area is enlarged to give space for the three pairs of crenu- 

 lated and perforated tubercles found in this region in all the spe- 

 cies of Hemicidaris. The upper part of the arese is occupied with 

 from 10-12 pairs of warty granules, which are smooth, deformed, 

 and set regularly in rows alternating with each other ; the in- 

 tervening surface of the ambulacral plates being occupied with 

 small ill-defined scattered granulations. The pores are disposed 

 in slightly oblique pairs, with a raised eminence between them ; 

 at the wide basal region of the avenues they fall into triple 

 oblique pairs. 



