55. 



primitive t^/pe or tliat they have been modified from the ordinary 

 type. 



Continuing from the quotation given above Pelseneer 

 says : "These common characters teach, at the same tim.e the 

 mutual relations of the Nuculidae and Solenomyidae which sho-ald 

 be united into a common group, contrary/ to the ideas up to the 

 present time, T^ich have placed the latter family v/ith the 

 Solenidae, near the Lucinidae, under the Anaticinacea, etc. 



If, on the other hand, comparisons be made betvT-een the 

 two families Nuculidae and Solenomyidae, it is proved that : 



1. ¥ith ITucula, the mantle is entirely open ventral ly, 

 between the two adductors, and that the margins are simple, with- 

 out tentacles. 



2. ¥ith the Nuculidae (Leda, Yoldia, etc) one sees 

 again that the retractors of the foot (columellaires) , form an 

 almost continuous series (without specialization), between the 

 two adduc t o r s . 



3. In the Nuculidal, the digestive tube presents a 

 pharyngeal cavity where two glandular pockets open. 



4. With ITuciila the heart is dorsal to the rectum. 



5. In ITucula the pleural ganglia reach their maximum 

 separation from the cerebral, in the sense that the cerebro- and 



