iS93- 



RECENT PROGRESS IN CONCHOLOGY. 



37 



and Argonauta, whose shell in those days was not thought to be the pro- 

 duct of the animal that occupied it. This arrangement, however, was 

 never really adopted by conchologists, and it was not until 1886 that 

 Boas (10) pointed out, on anatomical grounds, that the Pteropoda 

 could not be separated from the Opisthobranchiata. 



As one of the results of his researches in connection with the 

 preparation of the "Challenger" Reports on the Pteropoda (i I ) Pelseneer 

 was led to acknowledge the correctness of this conclusion, and it has 

 been subsequently accepted by Professor Lankester (12) and adopted 

 by Lang in his Lehrbuch (13). The latter authority, also, follows 

 Pelseneer in his classification of the Pelecypoda (14), or Lamellibran- 

 chiata, to use a later and less preferable term, to which we note with 



Heteropoda 



\ 



\ Platypoda 



Pulmonata 

 \ 

 \ 



Nudibranchia 



\ 



(Ctenobranchia) 

 \ 

 \ 

 Aspidobranchia 



\ Tectibranchia 



\/ 



(Euthyneura) 



Cephalopoda 



Actaeonidae 



\ / 



{Streptoneura) 



scaphopoda 



\ [Gastropoda] 



Aplacophora 



Polyplacophora 



Lamellibranchia 



/ 

 ./ 



Prorhipidoglossa 



[Amphineura] 



regret that our author reverts. These last he derives, as before, \vith the 

 Gastropoda from a common stock — the hypothetical Prorhipidoglossa, 

 but adds now as another branch from the same — the Scaphopoda. In 

 this he is in accord with Plate (15), who, however, places their branch 

 a little more directly on the main stem, between the off-shooting of 

 those of the Pelecypoda and Patella. In a subsequent note on the 

 genus Action (16), Pelseneer, agreeing with Bouvier (17), slightly 

 modifies his scheme, and considers that Actaon is not only the 

 common stock whence are derived the Pteropoda, Tectibranchiata, 

 and Pulmonata, but also the link between the Streptoneura ( = Proso- 

 branchiata) and the Euthyneura ( = Opisthobranchiata and Pul- 



