72 FOSSIL ASTEROIDEA. 



only plate of the dorsal sui'face wliicli is larger or moi'e conspicuous than the 

 remainder ; all are covered with a minute uniform granulation of a quite charac- 

 teristic appearance. The anus is almost central in position. It is surrounded 

 by a circlet of plates, amongst which is the centrale. The madreporite is, as 

 usual, situated in the next (clockwise) interradius, almost halfway between the 

 centrale and the margin. It is a triangular plate, the apex of the triangle being 

 a markedly acute ano-le. 



The arms are well produced. R : r : : 30 mm. + : 9 mm. Their breadth at the 

 base is mm. Radialia, adradialia, and dorso-lateralia extend into the base of the 

 arms. The dorso-lateralia soon disappear, but the adradialia persist as far as the 

 seventh or eighth supero-marginal plate. AVhen the adradials disappear the radialia 

 become larger. They ai^e at this point 1 mm. broad and I'l mm. long and 

 therefore appear almost square. 



The supero-marginalia are oblong plates of curiously uniform size in the portions 

 of the specimen preserved. They are 1-6 mm. long and from l'2mm. to 1-omm. 

 broad. The infero-marginalia are of the same length and are opposite to the 

 supero-marginalia. In lateral view the supero-mai*ginalia appear higher than the 

 inferior series. Both series are oi'namented with a number of small, fine a:ranules 

 which are uniformly distributed over their surfaces. 



The ventral surface is concave. The ventro-lateral plates are rhomboidal in 

 the region of the mouth. They become polygonal and crowded as they approach 

 the margin. Some of these plates extend into the base of the arms. Around the 

 edges of the plates spinelets are visible. The spines of the adambulacral plates are 

 still present. Unfortimately, it is not possible to make out their exact distribution. 

 The mouth-angle plates are not prominent. 



There is no trace in this species of such valvate pedicellariae as characterise 

 G. Comptoiii. 



Bemarls. — Gray compared this species with Civlaster, Agassiz.^ The rather 

 vague diagnosis of Ccchi.'^ter given l)y Agassiz renders exact identification impossible. 



Lorality and Sfr(ifi<jy(i2>ltical Position. — Upper Greensaud of Blackdown. Also 

 in the Upper Greensand at Folkestone (observed by Forbes). 



' Agassiz, 'Annales des Sciences Naturelles,' 1837. Trauslated in ' Annals and Magazine of 

 Natural History,' vol. i, 1833. 



