History of British Entomostraca. 39 



for the most part, enclosed within a testaceous covering, either in 

 the form of a buckler, or that of a bivalve shell. The second order 

 Psecilopoda embraces those insects which are not provided with or- 

 gans proper for mastication, and are almost all parasitical, living upon 

 fishes and other aquatic animals. The first order, the Brancho- 

 poda, is divided into two principal sections, the " Lophyropa and 

 Phyllopa." The first of these again is subdivided into three very- 

 natural groups or families, the " Carcinoida, Ostracoda, and Clado- 

 cera ;" while the second is subdivided into two. The Psecilopoda, 

 on the other hand, is composed of rather heterogeneous materials, and 

 many of the genera approach very much to the " Lernese," though, 

 according to Latreille, the presence of eyes, the faculty of changing 

 their skin, or even of undergoing a species of metamorphosis, and the 

 power which they possess of transporting themselves from one place 

 to another, by means of feet, establish a positive line of demarcation 

 between the Psecilopoda and Lernese.* The arrangement above- 

 mentioned has, since 1829, received from its accomplished author, 

 some modifications, which he published in 1831, in his " Cours 

 d' Entomologie," but which I have not seen. The last writer upon 

 the Crustacea, M. Milne-Edwards, in his work, half of which 

 only is as yet published, t has taken perhaps a more philosophical 

 view of the subject, and has proposed the following arrangement : 

 The great class " Crustacea" he divides into three sub-classes, the 

 characters of which are taken chiefly from the organization of the 

 mouth. The two first of these have an apparatus especially 

 provided for the laying hold of the substances destined for their 

 food, while the third has no such special organization, their masti- 

 catory organs being the same as their organs of locomotion. The 

 first sub-class is that of the Maxilles or those whose mouth is 

 furnished with organs for mastication, the second is that of the 

 Suceurs, or those whose mouth is furnished with an apparatus for 

 sucking, and the third is that of the Xyphosuriens, or those whose 

 organs of motion are the same as the organs of mastication, and 

 which differ in many other points also from the two first. The sub- 

 class Maxilles, he again divides into four legions, 1st, " Podop- 

 thal miens," containing the orders " Decapodes" and " Stomapodes ;" 

 2d, " Edriopthalmes," containing the orders, " Amphipodes," " Iso- 

 podes," and " Lamipodes ■;" 3d, " Entomostraces," containing the 

 orders "Ostrapodes," and" Copepodes;" and 4th, " Branchiopodes," 

 containing the orders " Cladoceres" and " Phyllopodes." The order 



* Regne Animal, vol. iv. p. 147 



f Histoire Naturelle des Crustacea, Suites a Buffon, torn. i. Paris, 1834. 



