10 BRITISH ENTOMOSTRACA. 



Monoculi and Binociili. Brisson, however, in his ' Regne 

 Animal,' * as early as 1756, had formed a distinct class 

 for the Crustacea, of which the Entomostraca formed a 

 part ; and Cuvier and Latreille, in their second Methods, 

 and in their subsequent publications, and all succeeding 

 authors, have adopted this arrangement, and have con- 

 tinued to place the Entomostraca with the great family 

 Crustacea, apart from the Insects. 



Latreille, in his ' Hist. Nat. gen. et part, des Crust.,' 

 1802, divides the great class Crustacea into two sub-classes, 

 the Entomostraca and Malacostraca. The Entomostraca 

 he subdivides into two sections — Thecata, those inclosed, 

 1st, in a shield-shaped, or, 2d, in a bivalve-formed shell or 

 covering, and Gymnota, those in which the body is nearly 

 or entu-ely naked. The Thecata he divides into four orders, 

 the Xiphosura and Pneumoneura, corresponding nearly to 

 the Binoculi of his first arrangement, and the Phyllopoda 

 and Ostracoda corresponding in part to his Monoculi. 

 The Gymnota he divides into two orders, the Pseudopoda 

 and the Cephalota, which include the remainder of his 

 Monoculi. In his ' Gen. Crust, et Insect.,' 1806, and in 

 his ' Consid. generates,' 1810, he follows the same ar- 

 rangement ; and Leach, in the ' Edinburgh Encyclopaedia,' 

 and again in the Supplement to the ' Encyclopaedia 

 Britannica,' adopts, in his articles on the Entomostraca, 

 one precisely similar, taking as the basis of his subdivisions 

 the covering or shell in which the animal is contained. 

 In the ' Diet, des Sc. Nat.,' 1819, this naturalist adopts, 

 however, the structure of the feet as the basis of sub- 

 division. He forms four orders : 1st, Paecilopoda, where 

 the feet in front are formed to walk and lay hold with, 

 and the others for swimming ; 2d, Phyllopoda, where the 

 front feet are formed like antennae, terminated by long- 

 setae, and the others formed for swimming ; 3d, Lophy- 

 ropoda ; and, 4th, Branchiopoda, in which all the feet are 

 formed for swimming, 



* Lc R("giic Auiinal, divis. cii 9 Classes, &c. 



