120 CRUS TACHA —PHRACAR TDA CHAP. 
related genera compose this family, of which Jlysis, Boreomysis, 
and Siriella may be mentioned. J/ysis 
oculata, var. relicta, 18 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 length, 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 beleves them 
to be of a primitive nature showing 
relationship to Nebalia, 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 may 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 
eae ee i eee limbs of the female and on 
Diastylis stygia, x 12. A, 2nd the last in the male. In the Cumidae 
seca eae Sala the four posterior pairs in 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 
Abi6=--=—-#: 
1 Sars, “ Crustacea of Norway,” iii., 1900. 
