210 Dr. T. Wright on the Cassidulidse of the Oolites. 



The base is more or less concave, most so in the pyramidal 

 varieties, and is slightly undulated; the ambulacra radiate in 

 straight lines from the mouth, and the interambulacra form 

 slightly convex pyramids between them. The mouth-opening is 

 excentrical and situated in a deep depression nearer the anterior 

 than the posterior border. 



Affinities and differences. — This species very much resembles 

 N. dimidiatus, but is distinguished from that species by its taper- 

 ing posterior lobes, which are more tumid in N. dimidiatus, by 

 the extent of the anal valley, which in N. clunicularis extends 

 from the disc to the margin, whilst in N. dimidiatus there is a 

 smooth portion of the test between the disc and the commence- 

 ment of the valley: from N. orbicularis this species is distin- 

 guished by its subquadrate form, increasing sides, and bilobed 

 posterior extremity ; it wants likewise the general tumidity so 

 characteristic of N. orbicularis, which it resembles in the length 

 of the anal valley. 



Locality and stratigraphical range. — We have collected this 

 Nucleolite from the upper ragstones of the Inferior Oolite of 

 Rodborough, Coopers, Birdlip, and Leckhampton Hills ; it is not 

 however a common species. It is found in the Great Oolite at 

 Minchinhampton and Cirencester, in the Cornbrash of Gloucester- 

 shire, Wiltshire, Northamptonshire, and Yorkshire : the Inferior 

 Oolite specimens are the most orbicular and depressed, the Great 

 Oolite ones are the smallest, and the Cornbrash are the most py- 

 ramidal in form. 



Its foreign distribution, according to Agassiz and Desor *, is 

 "Oxford d'Alencon, Courgains (Sarthe), Calc. h Polypiers de 

 Ranville, Coulie. Var. minor. Forest marble de Chatelcensoir." 

 Form latiporus, "Cornbrash de Meltingen (Cant, de Soleure), 

 Maiche (Doubs). Form gracilis, Ool. Ferrug. de Durrenast 

 (Jura Soleurois)." 



History. — It would carry us far beyond our limits to attempt 

 to trace the history of this species from Llhwyd to Agassiz ; but 

 even had it been otherwise it would have been unnecessary, as 

 this has been so ably done by Professor Forbes in his ' Memoirs 

 of the Geological Survey/ to the 1st Decade of which the reader 

 is referred for an excellent critical examination of the literature 

 of this species ; in the same work it is most elaborately figured 

 and correctly described. 



* Catalogue raisonne des Echinides : Annales des Sciences Naturelles, 

 tome vii. p. 153, 3 e serie. 



