KEY-TABLE. 



117 



5. No spine-pits present. 

 (A) (B) 



TEXT-FIG. 15. 



a. Proximal marginalia almost smooth ; distal 

 with granular rugosities arranged in a linear 

 series. N.radiatns. Text-fig. 15, (A) pro- 

 ximal marginal, (B) distal marginal. 



b. Marginalia with rugosities not arranged in 

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



TEXT-FIG. 16. 



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

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



1. Spine-pits on central raised area. 



(B) 



a. Central raised area smooth on both superior 

 and inferior marginalia. Spine-pits on 

 mfero-marginalia uniformly situated. M. 

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

 of marginal, (B) side view of marginal. 



TEXT-FIG. 17. 



(B) 



v.v,*/,y, iv,j 



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-margiual, 

 (B) infero-marginal. 



c. Central raised area of supero-marginalia 

 smooth in young, rugose in mature indi- 

 viduals. Lower Chalk form. M. cormdus 

 (see p. 124). 



-'-'- 



TEXT-FIO. 18. 



18 



