SYSTEMATIC ARRANGEMENT. 
11 
Lamarck, in his e Hist. Anim. sans Verteb./ 1818, 
divides the class Crustacea into two orders, the Hetero- 
branches and Homobranches. The first of these is 
divided into four sections, Branchiopodes, Isopodes, 
Amphipodes, and Stomapodes. The second is divided 
into two, the Macroures and Brachyures. The first 
section of the first order, viz. the Branchiopoda, includes 
all Mtlller’s Entomostraca, and all the genera known up 
to that time, except the genus Nebalia of Leach, which 
is placed in the first section of the second order, the 
Macroures. 
Latreille, in his last Method, in the ‘ Regne Animal’ 
of Cuvier, vol. iv, adopts a new arrangement, using for 
his principal subdivisions the organization of the mouth. 
He divides the Entomostraca into two orders, the 
Branchiopoda and Psecilopoda. The order Branchiopoda 
contains those genera which have organs proper for mas- 
tication, are possessed of branchiae attached to the feet 
or jaws, and are for the most part inclosed within a 
testaceous covering, either in the form of a buckler or 
that of a bivalve shell. The second order, Paecilopoda, 
embraces those which are not provided with organs proper 
for mastication, and are almost all parasitical, living upon 
fishes and other aquatic animals. The first order, the 
Branchiopoda, is divided into two principal sections, the 
Lophyropa and Phyllopa. The first of these again is 
subivided into three very natural groups or families, the 
Carcinoida, Ostracoda, and Cladocera ; while the second 
is subdivided into two, the Ceratophthalma and the 
Aspidiphora. The Paecilopoda, on the other hand, is 
composed of rather heterogeneous materials, and is divided 
into two families, the Xiphosura and Siphonostoma.* 
* Latreille appears to have been struck with the resemblance which the 
Lernese bear to some of the genera of the Siphonostoma ; but as he was then 
not aware, of what has since been discovered, that the young of the Lernese 
undergo a metamorphosis like that of the Cyclopidse and Caligidse, and that 
the adults have the faculty of changing their skin or moulting, he considered 
that the absence of these marks established a positive line of demarcation 
between them and the Entomostraca. 
