FROM THE CORNBRASH. 345 



the narrowest, and the posterior pair and single inter-ambulacrum are the same diameter ; 

 their upper surface is uniformly convex, and the plates are covered with tubercles, 

 set closely together (fig. 1 d). There are five or six rows on each plate, the areolas of 

 which are so nearly approximated that there are much fewer granules between them than 

 in the nearly allied E. ditnicularis ; the tubercles likewise are larger than in that species. 

 (Compare PI. XXIV, 1 e, with PI. XXXVI, fig. 1 d.) 



The upper surface of the single inter-ambulacrum is very much depressed to form the 

 anal valley, the sides of which slope obhquely inwards, and form an angle of 65° with the 

 base (fig. 1 a) ; the posterior border is much indented by this depression, and forms quite 

 a concave depression behind (fig. \ a, b). 



The apical disc is rather larger than in E. dunicularis ; it occupies the vertex of the 

 test, and is placed nearer the posterior than the anterior border. The four genital 

 holes are large and distinct, and the madreporiform body is not very prominent. 



The base is concave, and the small excentral mouth-opening (fig. 1 5) is situated 

 nearer the anterior than the posterior border ; the peristome is circular or subpentagonal, 

 with five rudimentary oval lobes. The poriferous zones lie in depressions, and 

 distinctly radiate from its circumference (fig. 1 b). The basal tubercles are larger than 

 the dorsal ; they are placed so close together that the areolas are separated only by single 

 rows of granules (fig. 1 b). 



Affinities and differences. — I have already pointed out the diagnostic characters by 

 which this species is distinguished from E. major, Agas., the nucleolite which most nearly 

 resembles it in form, size, and general outline. Its next nearest affinity is with E. dunicu- 

 laris, Lhwyd ; from this species it is distinguished, however, by its quadrate shape and 

 depressed dorsal surface, by the vsdde anal valley, with its oblique sloping sides and concave 

 posterior border. The apical disc is likewise situated behind the centre of the test, 

 and the tubercles are larger and more closely crowded together. The structure of the 

 anal valley and the excavated character of the single inter-ambulacrum serve at a glance to 

 distinguish it from E. scutatus, Lamk. 



Locality and StratigrapUcal position. — All the specimens that I know of this species 

 were collected by Mr. WiUiam Buy from the Cornbrash near Sutton-Benger, Wilts, 

 where it is extremely rare ; it occurs with the small gray variety of E. dunicularis, 

 associated with Holectypus depressus, Lamk., Acrosalenia Wiltoni, Wright, Acrosalenia 

 hemicidaroides, Wright, Stomechinus intermedius, Agas., Acrosalenia spinosa, Agas., 

 Avicida echinata, Sow,, Terebratula obovata, Sow., Terebratula lagenalis, Schloth., and other 

 well-known Cornbrash forms. 



