KEY-TA1{I>K. 



117 



5. No spiue-pits present. 



(A) 



(B) 



Text-pig. 15. 



((. Pro.\iiiial inargiualia almost smooth ; distal 

 with <,'raiuilari-iii,'osities arranged iu a linear 

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

 ximal marginal, (b) distal marginal. 



b. Marginalia with rugosities not arranged iu 

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



B. ilarginals with a ral}bet-edgo. Ealjbet-edge covered with small spine- 

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



(A) 



1. Spiue-pits on central raised area. 



(B) 



Text-kio. 17. 



(B) 



(A) 



-"3»r*r 



a. Central raised area smooth on both sufierior 

 and inferior marginalia. Spiue-pits on 

 infero-margiualia uniformly situated. M. 

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

 of marginal, (b) side view of marginal. 



h. Central raised area of supero-marginalia 

 rugose ; that of infero-margiualia smooth, 

 with spiue-pits iu form of network. M. 

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

 (b) iufero-margiual. 



c. Central raised area of supero-marginalia 

 smooth in young, rugose in mature indi- 

 viduals. Lower Chalk form. M. coriniliie 

 (see J). 124). 



Text-kio. is. 



18 



