ISOPODA. Ill 



versed. In other respects the groups proposed by M. 

 Edwards are natural ones, except the Asellotes, which 

 appear to us unnaturally increased by the introduction 

 of the genera Apseudes and Tanais. 



The classification of these animals by Mr. Dana, who 

 has bestowed an unusual amount of attention upon the 

 class Crustacea, demands a more extended notice. 



Rejecting the division of the Crustacea into, 1, those 

 with proper jaws ; 2, suctorial species ; and 3, those 

 with the basal joints of the feet acting as jaws,* as pro- 

 posed by Milne Edwards, on the consideration that too 

 great a stress has been laid upon the organs of mandu- 

 cation, Mr. Dana proposes to adopt three primary divi- 

 sions: 1, Podophthalmia ; 2, Edriophthalmia, comprising 

 the whole of the remainder of the Crustacea proper ; 

 and 3, the Cirripedia : dividing the Edriophthalmia into, 

 1, Choristopoda (or Tetradecapoda) ; 2, Trilobita; 

 3, Entomostraca ; and 4, Rotifera. 



In the revision of the classification of the Crustacea 

 given in the latter portion of his great work (founded 

 upon subsequently-acquired views of Cephalization and 

 consequent concentration or dispersion of forces), Mr. 

 Dana modified this arrangement of his primary groups, 

 giving five subclasses, namely — I. Podophthalmia (or 

 Decapoda, including Mysis and Squilla) ; II. Tetradeca- 

 poda — Order 1, Choristopoda; Tribe 1, Isopoda; Tribe 2, 

 Anisopoda ; Tribe 3, Amphipoda : Order 2, Trilobita, of 

 doubtful situation ; III. Entomostraca ; IV. Cirripedia ; 

 V. Rotatoria. 



Thus his Choristopoda are equivalent to Leach's Edri- 

 ophthalma. Here also, rejecting Latreille's order Leemo- 

 dipoda, Mr. Dana admits two prominent groups; the 



* Mr. Dana (Crustacea, p. 9), by a strange mistake, speaks of the basal 

 joints of the feet acting as legs instead of jaws. 



