FROM THE CORALLINE OOLITE. 351 



NucLEOLiTES DiMiDiATUs. Wright (pars), Annals and Magazine of Natural Hist., 2d series, 



vol ix, p. 300, 1851. 



— scuTATUs. Wright, Annals and Magazine of Natural Hist., 2d series, vol. xiii, 



p. 185, 1854. 



— — Forbes, Morris's Catalogue Brit. Foss., 2d ed., p. 84, 1854. 

 EcHiNOBRissus SCUTATUS, var. alongee. Desor, Synopsis des Echinides Fossiles, p. 267. 



« 



Test elongated, narrower before than behind ; convex above, concave below ; sides 

 tumid ; apical disc excentral, nearer the anterior border ; anal valley short and narrow, 

 reaching two thirds the distance between the posterior border and summit, with a 

 triangular undepressed space between its upper margin and disc ; posterior lobes obsolete, 

 posterior border only slightly grooved. 



Dimensions. — Antero-posterior diameter, one inch and three tenths ; transverse 

 diameter, one inch and three twentieths ; height, seven tenths of an inch. 



Description. — This urchin is very abundant in the Coralline Oolite of Malton, from 

 which rock it was first figured by Professor Phillips. Unfortunately he gave no description 

 of the species, and his figure represented only one view of the nucleolite. Professor 

 Edward Forbes, who carefully studied this form, gave the following diagnosis of its 

 characters : " N. amhitu ovato, antice rotundato, postice hilohato ; dorso convexo, apice 

 centrali, vertice sub-centrali, postice tumido ; ambulacris anguste lanceolatis ; sulco anali 

 prof undo, ovato ohtuso, superne abbreviata, lobis posterioribus tumidis ; ventre plus minusve 

 concavo. 



" This species rarely exceeds one inch in length, and varies greatly in the convexity of 

 its upper surface. The ovate anal sulcus, reaching about two thirds of the distance between 

 the posterior margin and the true summit, conspicuously distinguishes it from clunicularis, 

 with which it was confounded before being distinguished by Phillips." 



When Professor Forbes published the above ' Note on British Nucleolites ' appended 

 to the description of pi. ix, decade 1, of the 'Memoirs of the Geological Survey,' he 

 was not aware of the existence, in our Oolites, of N. scutatus ; it is therefore probable 

 that his diagnosis was framed to include some forms of that species. 



E. dimidiatus has an oval outline, the upper surface of the test is uniformly 

 convex ; the sides and anterior border are very tumid in some specimens, and moderately 

 so in others ; the posterior border is rounded and only slightly grooved by the sulcus. 



The ambulacral areas are narrow and lanceolate ; the single area and anterior pair are 

 narrower than the posterior pair, which are much longer and better developed than the 

 others. The poriferous zones lie in slight depressions of the test, their petaloidal portions 

 are wider than the homologous part of this species in E. scutatus, and there arc live to six 

 pairs of pores opposite each large plate. 



The inter-ambulacral areas are of unequal width, the anterior pair are the narrowest, 



46 



