INTRODUCTION. 



25 



periods. Thus, the affinities of the same three species may he 

 shown in the following comparisons : 



S. dicliotoma series. 



p. c. L r. 



S. dichotoma (Lamx.) 2 1 1 Jurassic. 



S. granulata, M. Edw. (non auct.} 2' 0' 1 1 Cretaceous. 



S. divaricata, Reuss 2' 0' 1' 0" Miocene. 



S. trahens, Couch (S. granulata, 



Johnst.) 2" 0" 1 2 Eecent. 



S. dicJiotomoides series. 



S. dichotomoides (D'Orb.) ... 

 S. phcata, D'Orb 



S. vesiculosa (Mich.) 



S. waltoni, Haime ... 

 S. longi.scata, D'Orb. 

 S. reussi, n. nom. 



... 1 2 1 Jurassic. 



... 1 2' 1 Cretaceous. (Ornamen- 

 tation differs.) 



... 1 2" 1 Miocene. 



S. waltoni series. 



... 1 2 Jurassic. 



... 1" 2 Cretaceous. 



2020 Miocene. 



Similarly we may contrast the Jurassic species of Proloscina 

 amongst themselves by a list of their formulas : 



P. eudesi, Haime 

 P.jacquoti, 

 P. desoudini ( ) 

 P. cunningtoni, Greg 

 P. rigauxi (Sauv.) 

 P. morinica (Sauv.) 

 P. liassica, Quenst 



4-7 



1-12 



1-2 



1-3 



1-12 



1-4 



3-5 



"We may also contrast the Proloscina species with those of a later 

 period, as follows : 



P. eudesi series. 



p. c. L r. 



P. eudesi, Haime ... ... 102 4-7 Jurassic. 



P. radiolitorum (D'Orb.) 1' 2 4-7 Cretaceous. 



P. jacquoti series. 



P.jacquoti, Haime 203 1-12 Jurassic. 



P. ramosa (Hag.) 2 2' 1-8 Cretaceous. 



P. dilatans (Johnst.) 2 3 2-8 Eecent. 



1 In these formulae r stands for the number of zooecia in a band. 



* Tn 



