48 MESOZOIC RADIATA. 



usual diameter about 5 lines) ; centre obscurely granular, ra- 

 diating lamellae very slender, close, minutely crenulated, alter- 

 nately larger and several shorter (number varies with the size 

 of the star, but always about twelve in a space of two lines at 

 the margin). 



In the very irregular size and shape of the stars and the great 

 number and delicacy of the lamellae, this agrees with the A. con- 

 fluens (Gold.), from which it differs in the flatness of the cells, 

 and in wanting the remarkable confluent character of that spe- 

 cies, the young cells developing their boundary ridges almost on 

 their first appearance. 



Common in the inferior oolite of Dundry. 



(Col. University of Cambridge.) 



Astrcea explanulata (M^Coy). 



Sp. Char. Corallum forming flat expansions, of nearly equal, 

 subrhomboidal, shallow cells, averaging 2 lines in diameter ; 

 radiating lamellae from twenty-six to thirty, thick, very ob- 

 scurely punctured or crenulated, about every third one reach- 

 ing to the impressed central point ; interstices very obtusely 

 angular. 



In the flat form of growth assumed by the masses, and in the 

 equality, shallowness and tetragonal form of most of the cells, 

 this strongly resembles the A. explanata (Gold.) of the Natheim 

 oolite ; but on comparison with authentic specimens of this latter, 

 I find the cells of our species average only half the diameter of 

 that, the radiating lamellae are little more than half the num- 

 ber, are much thicker and almost perfectly smooth. In num- 

 ber and thickness of the lamellae it more nearly approaches the 

 common A. helianthoides (Gold.), but differs in their compara- 

 tive smoothness and the more equal size and quadrate form of 

 the cells, &c. 



Common in the inferior oolite of Dundry and Bath. 



[Col. University of Cambridge.) 



Astrcea helianthella (M'Coy). 



Sp. Char, Corallum forming large depressed turbinate masses 

 (generally from 2 to 5 inches in diameter and 9 lines to 2 inches 

 high) with faint concentric wrinkles below, crossed by very 

 minute radiating striae ; upper surface flat, covered with small, 

 subequal, polygonal cells (diameter, or from centre to centre, 

 varying from 1- to 2 lines) with rounded boundaries and very 

 deeply excavated centres j lamellae about thirty-eight, eight or 

 nine of which reach the centre, of moderate, nearly equal thick- 

 ness, slightly rugged. 



