124 



FOSSIL OOLITIC ASTERIAD^. 



inter-ambulacral bones at their border carry tufts of small, spatulate, equal-sized spines, which 

 form a boundary for the ambulacra] furrows ; mouth surrounded by five ridge-like termi- 

 nations; ventral integument covered with numerous rows of elongated, spatulate spines. 



Dimensions. — Diameter of the ventral disc, one inch and eight tenths ; length of a 

 ray, about two inches and three tenths. 



Description. — This Star-fish has all the five rays gently bent, indicating a flexible 

 condition of the articulation of the mara;inal bones; this bending of the ravs is well 

 delineated in the drawing ; the everted ray exhibiting the same curvature, which proves 

 that the bending of the rays was dependent on the form of the articulating surfaces of the 

 marginal bones, and not on muscular contraction, seeing that it was persistent after death. 



The surface of the marginal plates, forty in number in the portion of the longest ray 

 remaining (and probably the part which is absent had twenty more), is closely covered 

 with small, flattened tubercles ; those on the ventral plates support short, spatulate spines, 

 which clothe the entire surface of the plates in an imbricated manner (fig. 1 c) ; the dorsal 

 marginal plates are likewise covered with similar flattened tubercles, and many of the small 

 spines which they supported are seen in situ ; at the distal border of the ventral series several 

 of the longer, thorn-like spines are seen which armed the border of the rays (fig. 1 (/). 



The everted ray exhibits in a very satisfactory manner the structure of its under 

 surface ; the ambulacral furrow is wide, and bounded by a series of small inter-ambulacral 

 bones (fig. 1 c), which carry combs of small, flat spines, with flattened terminations on 

 their lower edges. Tig. 1 c shows these tufts of spines hanging like festoons of fringes 

 along the border of the ambulacral fiu-rows (fig. I b and fig. 1 c). The inter-marginal 

 tegumentary membrane of the disc and dorsal surface of the rays was strengthened with 

 small ossicles, and the remains of the paxilte are strewed abundantly amongst these 

 calcareous pieces. 



The tegumentary membrane on the ventral surface of the disc was covered with long, 

 spatulate spines, which were disposed in rows in an imbricated manner; the under surface 

 of the rays had likewise ranges of short, flat spines, set in rows on the marginal plates, and 

 combs of spines on the inter-ambulacral bones, so that the under surface of this Star- fish 

 was everywhere clothed with small, spatulate spines ; the distal border of the ventral 

 marginal plates had a row of larger, thorn-like spines projecting outwards. 



The ventral surface of the disc is wide, and around its centre are five ridge-hke bodies, 

 with small tubercles on their surface (fig. 1 a); these bony processes might have been em- 

 ployed as jaws. 



Affinities and differences. — This species is nearly allied to Astrospecten PJiillipsii, 

 Forb., but the greater size of the disc, with the breadth and curved shape of the rays, distin- 

 guish these forms from each other. The structure of the marginal plates and the inter- 



