KEY-TABLE. 



115 



CHALK (CENOMANIAN-SENONIAN) SPECIES. 

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



A. Without a rabbet-edge. Gallidenna, Nymphaster, Pentagonaster. 



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

 c. With a distinct ridge. Artkraster. 



II. Marginals either hexagonal or rounded; very thick. Hadranderaster. 

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

 IV. Marginals breast-plate-shaped. Staurandemster. 



V. Miscellaneous 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. 



(A) 



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

 (B) 



TEXT-PIQ. 8. 



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

 Text-fig. 8 A. Variety with medium- sized spiue-pits 



(see p. 123). 



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

 p. 123). 



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. 



