I is 



FOSSIL ASTEROIDEA. 



2. No spiue-pits on central raised area. 



(B) 





Text-fig. 19. 



(A) 



a. Rugosities present on greater portion of surface 

 of supero-marginalia. M. rugatus. Text-fig. 

 19, (a) supero-marginal, (b) infero-marginal. 



b. Rugosities confined to inner edge of supero- 



marginalia or absent ; outer portion of plate 

 tumid, a. Plates oblong. M. uncatus. Text- 

 fig. 20, (a) supero-marginal, (b) infero-mar- 

 ginal. j3. Plates scpmre. M. qtiadratus. 



c. No rugosities present on the supero-marginalia 



which are not tumid on their outer portion, 

 ill. compadus. See PI. XXVI, fig. 3 b. 



Text-fig. 20. 

 N.B. — The infero-marginalia of the above species ai*e difficult to distinguish except by 

 their dimensions. The reader is advised to refer to the detailed description for these. 



II. 



c. Marginalia with a distinct ridge which has granular elevations along 



its base. 



(A) 



Arthraster 



(b) 



1. Upper surface of ridge smooth. A. Dlxoni. 



Text-fig. 21, (a) outer view of marginal, (b) 

 side view of marginal. 



2. Upper surface of ridge with spine-pits. A. cris- 



tatus. See PL XXIX, fig. 10. 



Text-fig. 21. 



-Plates either hexagonal or rounded ; very thick. Spine-pits form a distinct, 

 fine honeycomb marking. ILidraiide raster (see p. 125). 



There is only one species. H. abbreviatus. Text- 

 fig. 22, (a) outer view of marginal, (b) side 

 view of marginal. 



Text-fig. 22. 



