ARTHROPOD A. 



77 



Subclass III. ENTOM08TBACA. 



Body furnished with a carapace, consisting of one or two shells, 

 sometimes multivalve. Limbs jointed, setiferous. Branchiae 

 attached either to the limbs or to the oral appendages. Mouth 

 rnaudibulate. Sexes distinct. 



These are mostly minute and, with some exceptions, freshwater 

 animals, very prolific, animal feeders, and very rarely parasitic. 

 They undergo a moulting process as they grow, and some a me- 

 tamorphosis. Parthenogenesis is not uncommon. 



The Entomostraca of Milne-Edwards is confined to the two 

 orders Ostracoda and Copepoda. Dana includes in it his three 

 "suborders," G-nathostomata [Phyllopoda and Lophyropoda, the 

 latter containing Ostracoda and Copepoda], Cormostomata 

 [Pcecilopoda and Arachnopoda, the former comprising the 

 Epizoa only], and Merostomata [Xiphura]. Von Hayek confines 

 the Entomostraca to Epiz^a and Copepoda ; Clans and Schmarda 

 ignore the name. Excluding Epizoa, the term is here used in 

 its original significance. 



Branchiae, when present, attached to the mouth. 



Head and thorax covered by a carapace COPEPODA. 



Body enclosed in a two-valve shell OSTRACODA. 



Branchiae attached to the legs. 

 Eecent. 



Mandibles and maxillae simple. 



Feet few, not f oliaceous CLADOCERA. 



Feet many, foliaceous PHYLLOPODA. 



Mandibles and maxillae terminating in foot- * 



like appendages XIPHURA. 



Extinct. 



Body above three-lobed TRILOBITA. 



Body not lobed above EURYPTERIDA. 



Order I. COPEPODA. 



LOPHYROPODA. CROPHYROPODA. CYCLOPACEA. GNATUOSTOMATA. 

 EUCOPEPODA. 



Body covered by a single shell (carapace). Abdominal seg- 

 ments free. Four pairs of natatory legs. No branchia 1 . Tail 

 setiferous. 



In addition to the four pairs of legs, there is also a rudimen- 



