CALTGIDiE. 
261 
considered by some authors* as imperfect articulations. 
One on each side extends from the notch at the termina- 
tion of the narrow frontal plate to the sinus at the posterior 
part of the carapace, dividing it into two lateral segments, 
while a third runs across the centre of the body, connect- 
ing the other two, and forming an upper and a lower 
central segment. The upper, or anterior, may be called 
the cephalic, and the lower the thoracic region of the 
carapace. The former contains, attached to it, the an- 
tennae, eyes, organs of mouth, and foot-jaws ; the latter 
the first three pairs of natatory feet. 
The narrow plate, mentioned above as visible on the 
anterior edge of the carapace, is sometimes very distinct, 
and is prolonged laterally to a somewhat sharp point, 
which is detached from the margin of the carapace, and 
covers the insertion of the antennae. In tracing the parts 
of these little creatures analogous to the parts belonging 
to the higher Crustacea, we might consider this plate, 
with its lateral prolongations, as the representative of the 
first pair of antennae, here reduced to a single joint, and 
immoveably fixed to the carapace. 
The real antennae, (t. XXXIY, f. 5 b), corresponding to 
the second pair in the higher orders, are very short, and 
composed of two joints. The basal joint is inserted upon 
the edge of the carapace, immediately beneath the ter- 
minal point of the frontal plate. It is flattened in shape, 
and the upper edge is beset with short setae. The apical 
joint is narrow, nearly cylindrical in form, about two thirds 
of the length of the preceding, and is terminated by 
several short hairs. In many of the species we perceive, 
on the frontal plate, near its free Extremity on each side, 
and on the inferior surface, a remarkable organ (t. XXXIV, 
f. 5 a), consisting of a thin, nearly circular membrane, 
attached by its central portions, and in form of a cup, 
approaching somewhat in appearance to the sucking-disc 
of the Argulus. These were considered by Muller as the 
* Pickering and Dana, loc. cit. 
