120 



CRUSTACEA PERACARIDA 



related genera compose this family, of which My sis, Boreomysis, 



and Siriella may be mentioned. Mysis 

 ocnlata, rar. relicta, is a freshwater 

 form from the lakes of northern and 

 central Europe. 



Order II. Cumacea.^ 



The Cumacea are a group of small 

 marine animals rarely attaining an 

 inch in leng-th, which agree with the 

 Mysidacea in the characters noted 

 above as diagnostic of the Division 

 Peracarida ; they possess, however, 

 in addition a number of peculiar 

 properties, and Sars believes them 

 to be of a primitive nature showing 

 relationship to JVehalia, and possibly 

 to an ancestral Zoaea - like form. 

 They follow a habit similar to that 

 of the Mysidacea, being caught either 

 in the surface -plankton or in great 

 depths, many of the deep-sea forms 

 being blind. They are, however, not 

 true plankton forms, and they appear 

 to attain a greater development both 

 in point of variety and size in the 

 seas of the northern hemisphere. The 

 thoracic limbs niay be biramous, but 

 there is a tendency among many of 

 the genera to lose the exopodites of 

 some of the thoracic legs, an exopodite 

 never being present on the last few 

 „ CA r, 1 ■ PI thoracic limbs of the female and on 



Fig. 80. — Dorsal view of male 



T)iastyiisstygia,x\2. A,im\ the last in the male. In the Cumidae 



antenna ; Ab.6, 6th abdominal i.^ n . • • ■ i ii „ „ 



a,.i.en,iag.. (After Sars.) ^he four posterior pairs m both sexes 



have no exopodites. The first three 



thoracic appendages following the maxillae are distinguished as 



maxillipedes ; they are uniramous, and the first pair carries an 



' Sars, "Crustacea of Norway," iii., 1900. 



