KEY-TABLE. 



117 



5. No spine-pits present. 



(A) (B) 



(!},'■ 





Text-fig. 15. 



Proximal marginalia almost smooth ; distal 

 with granular rugosities arranged in a linear 

 series. N.radiatus. Text-fig. 15, (a) pro- 

 ximal marginal, (b) distal marginal. 



b. Marginalia with rugosities not arranged in 

 linear series. N. vmjosus. Text-fig. 16. 



Text-fig. 16. 



b. Marginals with a rabbet-edge. Rabbet-edge covered with small spine- 

 pits. Pedicellariae when present "winged" (see Text-fig. 7). 



(A) 



1. Spine-pits on central raised area. 



(B) 



a. Central raised area smooth on both superior 

 and inferior marginalia. Spine-pits on 

 infero-marginalia uniformly situated. M. 

 Parlcinsoni. Text-fig. 17, (a) outer view 

 of marginal, (b) side view of marginal. 



Text-fig. 17. 



(A) 



(B) 



"., 



Central raised area of supero-marginalia 

 rugose ; that of infero-marginalia smooth, 

 with spine-pits in form of network. M. 

 Hunteri. Text-fig. 18, (a) supero-marginal, 

 (b) infero-marginal. 





'.' c C * c 





Text-fig. 18. 



c. Central raised area of supero-marginalia 

 smooth in young, rugose in mature indi- 

 viduals. Lower Chalk form. M. cornutus 

 (see p. 124). 



18 



