DEC APOD A OR CRABS, LOBSTERS, ETC. OOO 



Having now made the student acquainted with several 

 classifications of the Crustacea, we have decided to adopt, 

 for our present purposes, the classification proposed by 

 Professor J. D. Dana, who recognizes only three Orders : 



1. DECAPODA or Ten-footed Crustaceans, with only five foot-seg- 



ments; as Crabs, Lobsters, Craw-fishes, Shrimps, Prawns, etc. 



2. lETRADECAPODA or Fourteen-footed Crustaceans, with seven 



foot-segments ; as Sand-fleas, Wood-louse, etc. 



3. EtfTOMOSTRACA O r Insect-like Crustaceans, with the body 



defective as to segments and feet ; as the Horse-shoe Crab, 

 Daphnia, Cypris, Cyclops, Barnacles, etc. 



SUB-SECTION II. 

 THE ORDER OF DECAPODA OR CRABS, LOBSTERS, ETC. 



As already indicated, the Crabs, Lobsters, Crawfishes, 

 Shrimps, Prawns, etc., have each five foot-segments ; that 

 is, five segments which bear a pair of so-called feet ; hence 



8. Copepoda, as Cyclops, etc. 



9. Ostrapoda, as Cypris, etc. 



10. Araneiformes, as Pycnogonon, etc. 



11. Syphonostom.i, as Caligus, etc. 



12. Lernaeiformes, as Lernaea, etc. 



13. Xyphosura, as Limulus. 



Dr. A. S. Packard, jr., writes me that he is inclined to classify the 

 Crustacea essentially thus : 



SUB-CLASS I. SUB-CLASS II. 



Decnpoda, 



Tetradecapoda, 



Nebaliadse, 



Pliyllopoda, 



Cladocera, 



Ostracodu, 



Copepoda (including Sipbonostoma), 



Cirripedia. 



t Trilobata, 

 1 Merostomata. 



