HIGHER CRUSTACEA OF NEW YORK CITY 129 



H e t e r o m y s i s f o r m o s a Smith is still smaller, males meas- 

 uring 6 mm and females 8 mm. The first pair of legs differ from 

 those of Mysis in having the terminal portion, which is multiarticu- 



Fig. 2 Mysis stenolepis (Modified from Verrill) 



late in that genus, composed of but three joints. The males are 

 colorless and transparent and the females rose-colored. 



Found in colonies, often in the dead shells of bivalve mollusks. 



Order 3 DECAPODA 



Malacostraca in which the head and thoracic segments are united 

 to form a cephalothorax, which is usually covered by a carapace. 

 The first three pairs of thoracic appendages are maxillipeds, while 

 the following five pairs are, as the name Decapoda implies, the 

 walking legs. In these the exopodite or outer branch of the typical 

 crustacean limb has disappeared, leaving the leg uniramous. The 

 first leg is usually larger than the others and by the growth of the 

 penultimate segment, forms a claw or chela. 



They breathe by gills which are hollow outgrowths from the bases 

 of the thoracic legs or of the thoracic wall and which are covered 

 by the carapace. The eyes are stalked. 



The Decapoda is a large group and contains the largest and most 

 striking of the Crustacea and has consequently been the most 

 studied. The literature is therefore extensive ; but besides the works 

 already referred to under Crustacea any other important ones will 

 be mentioned under the separate species. 



The Decapoda are divided into two suborders : a Macrura, 

 b Brachyura. 



