XX PREFACE. 



MOLLUSCA. 



BKANCH. EUCEPHALA. 

 GRADE A. LIPOGLOSSA. 



Class. Scolecomorpha (Neomenia). 



GRADE B. ECHINOGLOSSA. 



Class 1. Gastropoda,* 



2. Cephalopoda. f 



3. Scaphopoda. 



BRANCH. LIPOCEPHALA. 



Class 1. Tentaculibranchia (Polyzoa). 



2. Spirobranchia (Brachiopoda). 



3. Lamellibrancliia. 



The pliyla Enteropueusta, Cliastognatlia, and Nematoidea, containing 

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

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



* Includes the Chitons as a separate archaic grade " Amphomoea," the remaining 

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

 " Cochlides." 



f Includes Siphonopoda (Cuttles and Nautilus) and Pteropoda. 



E. EAY LAXKESTEK, 



Exeter College, Oxford. 



Septemher, 1878. 



