3o6 REPORT OF NEW JERSEY STATE MUSEUM. 



usually contained in a pouch or marsupium, formed generally of 

 certain number of lamelliform leaflets issuing from bases of legs. 

 Incubatory lamellae sometimes wanting. Young pass within mar- 

 supium of female through one or more so-called pupa states be- 

 fore hatching. Young also sometimes hatched in very im- 

 mature condition, and not attaining, till after very complicated 

 free metamorphosis, characteristic adult form. 



Four families are admitted, as the Lophogastridae, Eucopiidae, 

 Euphausiid^e. and the single remaining one represented, so far, 

 in our limits. 



Family MYSIDvE. 



The Opossum Shrimps. 



Carapace usually rather small, its hind part only loosely cover- 

 ing trunk, segments of which distinctly defined, though very 

 narrow and crowded together in dorsal part. Maxillipeds strong, 

 exopodite well developed and natatory, epipodite lanceolate and 

 projecting within branchial cavity. First pair of legs modified 

 gnathopoda. Remaining legs uniform, and generally rather 

 feeble, terminal part usually subdivided into short setiferous 

 articulations and dactylus usually small or absent. No true 

 branchiae present. Marsupium usually formed of only two or 

 three pairs of incubatory lamellae issuing from bases of hindmost 

 pair of legs. Female caudal limbs quite rudimentary, not formed 

 for swimming. In male caudal limbs either natatory or some 

 modified to serve as copulative organs. Inner plate of uropod 

 generally contains within its base peculiarly developed auditory 

 apparatus. Development without any free metamorphosis. 



Genera about twenty-eight. 



Genus MYSIS Latreille. 



Plate go, Figure 2. 



Mysis Latreille, Hist. Nat. Crust., VI, 1803, p. 282. Type Cancer pedatus 

 Latreille, first species. 



