KEY-TABLE. 



115 



Chalk (Cenomanian-Senonian) Species. 

 I. — Marginals four-sided, with sides rectilinear or almost rectilinear; broad. 



a. Without a rabbet-edge. Oalliderma, Nymph-aster, Pentagonaster. 



b. With a rabbet-edge. Metopaster, Mitraster. 



c. With a distinct ridge. Artkraster. 



IL— Marginals either hexagonal or rounded; very thick. Kadranderaster. 

 III. — Marginals wedge-shaped, high, spine-pits very shallow or absent. Pycinaster 

 IV. — Marginals breast-plate-shaped. Stauranderaster. 



V . — Miscella neous plates . 



I. — Marginals four-sided, with sides rectilinear or almost rectilinear. Pedi- 

 cellarise when present of a simple bi-valvate character. 



a. Without a rabbet-edge. Galliderma, Nymphaster, Pentagonaster. 



1. Spine-pits shallow, hexagonal, giving a honeycomb appearance. 



(A) (B) 



: .1 



•«** 



a. Honeycomb medium or fine. C.Smithise (see p. 123). 

 Text-fig. 8 a.— Variety with medium-sized spine-pits 



(see p. 123). 

 Text-fig. 8 b. — Variety with fine spine-pits (see 

 p. 123). 



Text-fig. 8. 





b. Honeycomb coarse. N. Coombii. Text-fig. 3, p. 113. 



c. Honeycomb confined to a portion of the plate (or 

 absent). P. obtusus. Text-fig. 9. 



Text-fig. 9. 



