290 ENALLASTER 



The tubercles are very small, and developed chiefly on the sides and base (fig. 1 b), 

 on the convex upper surface they are nearly absent (fig. 1 a) ; they are largest on the 

 anterior and lateral portions of the base (fig. 1 b), and on the plastron they are more 

 regularly arranged ; the miliary granules are very small, and set closely together over 

 the surface of the plates and around the tubercles, as seen in fig. 1/, where two large 

 plates and a portion of one of the ambulacral areas is magnified three diameters. 



Affinities and Differences. — It is distinguished from Enallaster Greenovii by a smaller 

 and narrower anteal sulcus, and by a difference in the structure of the antero-lateral 

 ambulacra, the size of the poriferous zones, and the form of the pores therein. 



Locality and Stratigraphical Position. — This species has been collected from Horse- 

 ledge Point, near Shanklin, Isle of Wight, from beds of Lower Greensand, where it is 

 very rare. I have found it in beds of the same age at Atherfield, and it is a leading 

 fossil of these beds in the Island. It has been collected from the Lower Greensand at 

 Hythe. My friend M. De Loriol gives La Presta (Neuchatel), Sainte-Croix (Vaud.), as 

 localities in Switzerland, where it is collected from the yellowish marl belonging to the 

 Stage Aptien inferieur. 



Enallaster Greenovii, Forbes, 1852. PL LXIV, figs. 2 a—f, 3 a— d. 



Hemipneustes Greenovii, Forbes. Mem. Geo). Surv., Decade iv, pi. v, 1852. 



— — — In Morris' Catalogue British Foss., 2 ed., p. 82, 



1854. 

 Enallaster Greenovii, d'Orbigny. Paleont. Franchise, Terrains Cretaces, tome vi, 



p. 183, pi. 849, 1855. 

 — — Dteor. Synopsis des Echinides Foss., p. 358, 1858. 



Diagnosis. — Test cordiform, enlarged and sinuous before, contracted and truncated 

 behind ; upper surface convex, and declined towards the anterior border. Anteal sulcus 

 large, and wider in the middle. Antero-lateral ambulacra long, biflexed; poriferous 

 zones unequal ; internal row formed of small, simple, close-set pores. Postero-lateral 

 pair of short zones equal ; posterior border obliquely truncated ; periprocte in the upper 

 third. 



Dimensions. — Fig. 1. Antero-posterior and transverse diameters 1 inch and 4 twelfths ; 

 height 1 inch. 



Fig. 2. Antero-posterior and transverse diameters 1 inch and 1 twelfth ; height 

 8 twelfths of an inch. 



Description. — This interesting Urchin has a regularly cordate outline, nearly as wide 

 as long, rounded and sulcated anteriorly, and bluntly truncated posteriorly. Its tumidity 



