284 TWENTIETH KEPORT ON THE STATE CABINET. 



These features of the ventral side have been ascertained by removing a 

 portion of one of the rays. 



Geological formation and locality. The specimen figured is from the 

 Trenton limestone at Trenton falls. I have seen another specimen from the 

 same neighborhood. 



PaL^ASTER SHiEFFERI (n. S.). 



PLATE IX, FIG. 1. 



Body of about medium size, composed of five tapering, acutely pointed 

 rays, which, in the specimem examined, measure seven-eighths of an inch 

 from the centre of the disc to the extremity. The lower side of the ray 

 is formed of two ranges of plates bordering the ambulacral groove. The 

 marginal range consists of moderately convex plates which gradually 

 decrease in size from the base to the extremity of the ray, twenty-two or 

 twenty-three in number, besides a small terminal one at the angle of the 

 range ; each plate of the marginal range is marked on its outer surface 

 by a comparatively large cicatrix for the attachment of a strong spine. 

 The inner range of plates ( adambulacral ) are somewhat smaller, about 

 the same in number, alternating with those of the marginal range, the 

 basal pair ( oral plates ) are elongate-triangular, and slightly constricted 

 near the middle. 

 Ambulacral areas narrow, Composed of a double range of poral plates, 

 which at the middle of the ray are about- of equal length and breadth. 

 Pores not observed. 

 Upper surface of the ray composed of three ranges of subnodose plates, 

 the outer ranges bearing a strong spine on each plate : the central range 

 apparently destitute of spines. 



This species differs from P. {Asterias) antiqua, Troost, in the more 

 slender and acutely pointed rays, and in the smaller marginal plates, the 

 basal one of which is quite different in form, that one being triangular with 

 the apex towards the axil of the ray. The ambulacral range also differs in 

 number of plates ; Troost's species having about twice as many in the 

 marginal range. 



It differs from Palceaster jamesi (= Palasterina jamesi*), Dana (Amer. 

 Jour. Sci. n. s.. Vol. xxxv, p. 295), in the form of the rays, the marginal 

 plates, and many other important characters, according to the figures given 

 by Mr. Dana. 



Geological formation and locality. In shales of the Hudson-river group, 

 Cincinnati, Ohio. From Mr. D. H. ShuEFFER. 



* This is not a Palasterina, having no disc-plates filling up the angles, as in the 

 typical species, and as required in the generic description given by Mr. Salter, and 

 f*)llowed by Mr. Billings, Can. Org. Rem. Dec. iii, p. 76. 

 4 



