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CHAPTER XIX. 



CRUSTACEA (Concluded). 



MALACOSTRACA. 



THE Malacostracous Crustaceans are distinguished by the pos- 

 session of a definite number of body-segments, seven somites 

 generally going to make up the thorax, and an equal number 

 entering into the composition of the abdomen (counting the 

 telson as a somite). The Malacostraca are divided into two 

 primary sections, termed respectively EdriophtJialmata and 

 Podopkthalmata, according as the eyes are sessile or are sup- 

 ported upon eye-stalks. 



DIVISION A. EDRIOPHTHALMATA. The division of the 

 Sessile - eyed Crustaceans comprises those Malacostraca in 

 which the eyes are not supported upon stalks or peduncles, 

 and there is mostly no carapace. The eyes are sometimes 

 compound, sometimes simple, and are placed on the sides 

 of the head. The head is almost always distinct from the 

 body ; and there are typically seven pairs of feet in the 

 adult. (Hence the name of Tetradecapoda applied to this 

 division by Agassiz.) The Edriophtlialmata include the 

 orders Lcemodipoda, Amphipoda, and Isopoda, of which the 

 two latter are alone known in a fossil condition. 



ORDER AMPHIPODA. 



Small Crustaceans in which the respiratory organs have the 

 form of membranous vesicles attached to the loses of tlie thoracic 



