STRUCTURAL RELATIONSHIP 315 



Phylum Mollusca. 



Class I. Pelecypoda or Lamelli- 

 branchiata mussels, oysters, 

 and other bivalves. 

 Class II. Gasteropoda univalves or 



shell-less mollusks. 



Class III. Cephalopoda squids, 

 devil-fishes, etc. 



Phylum A rthropoda. 

 Jointed animals. 



Class I. Crustacea crabs, lob- 

 sters, cray-fish, barnacles, 

 etc. 



Class II. Onychophora centipede- 

 like. 



Class III. Myriapoda centipedes, 

 etc. 



Class IV. Hexapoda insects. 



Class V. Arachnida spiders, 

 scorpions, etc. 



2. With a notochord. 

 Phylum Chlordata. 



Sub-phylum I. Atriozoa. 



Class I. Urochordata (Tunicata). 

 Class II. Cephalocordata (A m p h i- 

 oxus). 



Sub-phylum II. Vertebrata. 



Class I. Pisces fishes. 



Class II. Amphibia (Batrachia) 

 frogs, toads, salamanders. 



Class III. Reptilia lizards, croco- 

 diles, alligators, tortoises, 

 snakes. 



Class IV. Aves Birds. 



Class V. Mammalia mammals. 



