118 



FOSSIL ASTEROIDEA. 



2. No spine-pits on central raised area. 

 (A) (B) 



a. Eugosities present on greater portion of surface 

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

 19, (A) supero-marginal, (B) infero-marginal. 



TEXT-FIG. 19. 



b. Eugosities confined to inner edge of supero- 



marginalia or absent; outer portion of plate 

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

 fig. 20, (A) supero-margiual, (B) iufero-mar- 

 ginal. /3. Plates square. M. quadratus. 



c. No rugosities present on the supero-margiualia 



which are not tumid on their outer portion. 

 M. compactus. See PI. XXVI, fig. 3 b. 



TEXT-FIG. 20. 



N.B. The infero-marginalia of the above species are difficult to distinguish except by 

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



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

 its base. Arthr aster. 



(A) (B) 



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



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 PI. XXIX, fig. 10. 



TEXT-FIG. 21. 



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

 fine honeycomb marking. Hadranderaster (see p. 125). 



(A) 



(B) 



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

 fig. 22, (A) outer view of marginal, (B) side 

 view of marginal. 



TEXT-FIG. 22. 



