18 
ORCHESTIIDiE. 
The eyes are large, irregularly round, and placed near 
the top of the head. The upper antennae are so small 
that they seem almost rudimentary. The lower antennae 
in the male are long, sometimes two-thirds the length 
of the animal ; in the females and young males they 
are much shorter. The peduncle is longer than the fla- 
gellum, and appears to consist of but three articulations, 
the two basal ones being fused into the frontal wall of the 
head, a circumstance which forces the superior antennae and 
organs of vision nearly to the top of the head, a position 
not common in the Amphipoda. The olfactory denticle 
is wanting. The organ of smell probably undergoes some 
change to meet the altered condition of the existence of 
the animal from that of marine Crustacea generally. 
The mandibles are powerful organs, armed at the biting 
edge with teeth, formed more for tearing than for cutting; 
below which a second row of denticles is fixed upon a 
plate, which is movable. A few strong hairs or spines, 
curved inwardly, are situated between the incisive margin 
and the molar or grinding tubercle. This last is a 
prominence at the inner base of each mandible, and is 
crowned by very minute denticles, and corresponds with 
a similar grinder in the opposite jaw. By the joint action 
of these two molar tubercles an imperfect mastication is 
effected . 
The foot-jaws are not unguiculate — that is, the last ar- 
ticulation does not terminate in a sharp, nail-like extre- 
mity, but ends obtusely, the tip being fringed with short 
hairs. A squamiform plate is developed from three of 
the articulations, of which the first, the most internal, is 
the largest, and is furnished at the extremity with three 
small stout spines or teeth. The apparatus which com- 
poses the mouth projects anteriorly beyond the head, by 
which means the animal can the more easily gather its 
