SOME OTHER CRUSTACEA. 



223 



always small, for a magnificent form of large size occurs in 

 the Arctic Ocean, and with the Gorgon-headed starfish 

 (Asteroplnjtori) and some other beautiful creatures, rewards 

 the zeal of the investigator of that chilly sea. 



KEY FOR IDENTIFICATION OF MYSIM1. 

 Order SCHIZOPODA. Crustacea with eight similar pairs of bi- 

 ramose thoracic legs. 



Fam. MYSIDJB. Gills are absent. Auditory organ present in the 

 tail. 



Antennal scale twice as long 

 as peduncle of antennae. 

 Telson cleft M. flexuosa. 

 Antennal scale three or four 

 times as long as peduncle. 

 Telson entire M. milgaris. 

 Antennal scale same length 

 as peduncle. Telson short, 

 cleft for one-quarter its 

 length, upper half without 

 spines M. lamornce. 



Outer branch of uropods \ 

 one-jointed, and fur- I ,, . 

 nished with bristles on f Mysis 

 its outer margin . . j 



Outer branch of uropods 

 two-jointed, first joint 

 with spines, but not 

 bristles, on its outer 

 margin 



- Siriella 



Antennal scale same length 

 as rostrum S. armata. 



OUTLINE CLASSIFICATION OF LITTORAL CRUSTACEA. 



Sub-class MALACOSTRACA. Body with nineteen segments. 

 Section A. Forms with stalked eyes. 

 Order 1. DECAPODA (see p. 208). 

 Order 2. SCHIZOPODA. Eight pairs of similar biramose feet. 



Fam. MYSID.E. Auditory organ in tail. 

 Section B. Forms with sessile eyes. 

 Order 1. ISOPODA. Body flattened, appendages of abdomen, 



respiratory plates. 

 Only one form, Idotea tricuspidata, has been described 



in the text. 

 Order 2. AMPHIPODA. Body compressed, abdomen usually with 



six pairs of legs. 



In the text three sandhopper-like forms have been 

 described, as well as a member of the family 

 Caprellidse, in which the abdomen is greatly 

 reduced. 



