THE CLASSIFICATION OF CRUSTACEA 39 



subclass in the system of classification here adopted, 

 are nearly all microscopic animals, and are found 

 abundantly in fresh water as well as in the sea. The 

 carapace forms a bivalved shell, which completely 

 encloses the body and limbs, and is often sculptured 

 in an elegant fashion. The Ostracoda are remark- 



FIG. 14 Cyclops albidus, A SPECIES OF COPEPOD FOUND IN 

 FRESH WATER. (After Schmeil.) 



Female specimen carrying a pair of egg-packets. The actual 

 length is about one tenth of an inch 



able for the very small number of their appendages. 

 There are not more than two pairs of limbs behind 

 the maxilla. Most of the species are included in two 

 orders, the Myodocopa and the Podocopa, of which 

 the former may generally be distinguished by a 

 notch in the anterior part of the margin of the shell 

 (Fig. 13, A, ri). In the Podocopa the margin is entire. 



