xs PREFACE. 



MOLLUSOA. 



BRANCH. EUCEPHALA. 

 GRADE A. LIPOGLOSSA. 



Class. Scolecoinorpha (Neomeiiia). 



GRADE B. ECIIINOGLOSSA. 



Class 1. Gastropoda.* 



2. Cephalopoda.! 



3. Scaphopoda. 



BRANCH. LIPOCEPHALA. 



Class 1. Tentaculibranchia (Polyzoa). 



2. Spirobrauchia (Brachiopoda). 



3. Lamellibranchia. 



The phyla Enteropneusta, Chsetognatha, and Nematoidea, containing 

 respectively the genus Balanoglossus, the genus Sagitta, and the various 

 families of thread-worms, do not admit of subdivision into classes or orders. 



* Includes tbc Chitons as a separate archaic grade " Amphomoca," tho remaining 

 Gastropoda, all of which are asymmetrical, being placed in a higher grade as 

 " Cochlides." 



t Includes Siphonopoda (Cuttles and Nautilus) and Pteropoda. 



E. KAY LAKKESTEE, 



Exeter College, Oxford. 



September, 1878. 



