I915 A^O. 12. THE STROPHOMENIDAE OF THE KRISTIANIA REGION. 97 



Ol" interest to consider different questions concerning their systematic 

 value as it appears to the present writer. 



The group of terms, the indépendant value of which as generic names 

 are questioned, are just those which by many European authors have 

 been included in Strophomena Blaix\-. As to generic terms like Chrisii- 

 ania, Triplecia and Streptis no objection at all ought to be made, since thev 

 really each represent a very characteristic group of species of well 

 defined type, differing strongly from all others. Also Plectanibonites 

 constitutes a well distinguished group, though showing much more varia- 

 tions than the others, as has just been stated. 



As to the rest of the Strophomenids with which we have been deal- 

 ing in this paper, they have really many features in common, in exterior 

 as well as interior characters. The former are too well known to need 

 to be repeated here. As to the latter there certainly are both in ventral 

 and dorsal valves differences, most of which, however, cannot be said to 

 be very important. 



Only the type of shell, for which 1 have proposed the generic term 

 Palaeostrophoniena, shows with its Or////_--like cardinal process a highly 

 differing interior. 



Of the other large Strophomenids we find in Leptaeua in the sense 

 of Hall and Clarke and in Schliche rtella a series of external and internal 

 characters that make them rather well defined groups, the former however 

 strongly related to Rafinesquiua. the latter to the younger Orthotetes 

 Fischer. 



When proceeding to the remaining genera and subgenera of Stropho- 

 menids treated here. Rafiuesqiiitia, Biachvpriou, Stropheodonta, Strophomena, 

 Amphistrophia, and Strophonella the question is more complicated. 



Hall and Clarke in their »Introduction to the studv of the Genera of 

 Palaeozoic Brachiopoda= when dealing with the genus Stropheodonta, seem 

 to assume this group to be no further development of Rafinesquina since 

 they write (Vol. I p. 289] : «Its earliest members [Brachyprion] appeared 

 while Rafinesquina still existed, but the advent of the tj'pical Stropheodontas 

 was preceded by the decline and extinction of the Rafinesquinas- . Deal- 

 ing with Strophonella the same authors write (p. 291) that -The shells 

 included in this genus are essentially Stropheodontas with the relative 

 convexity of the valves reversed. It is evident from a careful inspection 

 of any well-preserved example of Strophonella, as alread}- shown fi-om a 

 study of very young individuals of 5. striata. Hall, that in early stages 

 of growth the convexit}* of the valves is normal, reversion of convexity 

 Vid.-Selsk. Skrifter. I. .M.-N. Kl 1915. .No. 12. 7 



