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HEMIASTER. 



Hemiaster Morrisii, Forbes, 1854. PI. LXI, fig. a — I. 



Spatangus prunella, Mantell. Geology of Sussex, pi. xvii, figs. 22, 23,. 



1822. 



Hemiaster — Besor. (pars) Cat. raisonee, p. 122, 1847. 



Echino spatangus cordiformis, Mantell (pars). Geol. Sussex, p. 108, 1822. 

 Spatangus complanatus, Mantell. Medals, p. 355. 



Hemiaster punctatus, d'Orbigny. Pal. Franc. Ter. Cret., pi. 886, 1854. 



— Morrisii, Forbes. Morris, Cat. Brit. Foss., 2nd ed., p. 81, 



1854. 



— — Woodward. Mem. Geol. Surv., decade v, pi. ix, 1856. 



Diagnosis. — Test oval, polygonal, or cordiform, inflated, obtusely rounded before and 

 obliquely truncated behind, sides nodulated; ambulacra straight, narrow, moderately 

 depressed, anterior pair twice as long as posterior, anteal sulcus short, shallow, dorsal ; 

 apical disc excentral backwards ; vertex near posterior border, which is flat and obliquely 

 truncated ; periprocte oval, supra- marginal ; base convex, with a slight depression near the 

 mouth, which is bilabiate and opens near the border; fasciole narrow, distinct, closely 

 surrounding the petals. 



Dimensions. — Antero-posterior diameter one inch and six tenths ; breadth one inch 

 and five tenths ; height one inch. 



Descrifjtion. — This Urchin has been long known to collectors of Cretaceous fossils by 

 many incorrect names. I have now figured it with ample anatomical details for the first 

 time, which for the future will make it impossible to mistake it for any other. 



The outline is oval, slightly polygonal, or inclining to a cordate shape ; the anteal sulcus 

 is broad and obscure, and impresses slightly the anterior border, which is obtusely rounded 

 and sometimes flattened; the posterior border is obliquely and flatly truncated, and 

 slopes at an angle of 70° ; sometimes this border becomes slightly concave in large shells, 

 and it is conspicuously so in three specimens in my collection. 



The ambulacral petals are small and moderately depressed, the anterior incline 

 45°; are nearly twice as long as the posterior pair (fig. 1 a) ; the poriferous zones are 

 narrow, and the pores form oblique transverse slits in them ; the single area is about same 

 length as the anterior, and is lodged in the anteal sulcus ; there are from twelve to fourteen 

 pairs of pores in each zone, with a prominent granule between each of the pores forming 

 a pair (fig. 1 a) ; the anteal sulcus widens out and disappears at the anterior border. 



The inter-ambulacral areas present a remarkable nodulated appearance in this species ; 

 in each area there are two rows of these elevations ; those at the sides are seen in 

 fig. 1 a, c ; in the front in fig. 1 e ; and the back fig. 1 d ; in fig. 1 h the appearance 



