236 
SUPPLEMENT 
proper. There is an upper lip, two large mandibles, two pairs 
of jaws, and a tongue. The caligi and some entomostraca of 
the neighbouring genera, are provided with a bill or sucker, 
formed of the union of two lips, and two very small mandibles, 
and with many of these (cecrops) M. Latreille has recognized, 
besides the bill, three pairs of jaw- feet. 
Independently of the antennae, &c. the head of some Crus- 
tacea is provided with certain prolongations, to which different 
names have been assigned. Thus, in many decapods, the por- 
tion of the carapace which is situated between the eyes, is 
more or less advanced, and takes the name of rostrum. Its 
dimensions vary, and it is sometimes bifurcated, sometimes 
denticulated, and sometimes spiny. 
In ancceus the head of the males is provided with two large 
projections, which very much resemble mandibles, but do not 
perform their functions, and there are two on the head of 
branchipes, resembling the mandibles of the lucanus cervits , 
and intended to seize the female in the act of coupling. 
Concurrently with these are two soft productions, spiral, in the 
form of a proboscis, which are situated between the others, 
and a little underneath. The first of these appendages are 
also found with females, but are much more simple and less 
voluminous, and the others do not exist. 
When the anterior edge of the head is not prolonged to form 
a rostrum, the interval separating the eyes assumes the name of 
front ox forehead, and sometimes that of hood (Fr. Chaperon .) 
The forehead is remarkable in the crabs and other brachyurous 
decapods, sometimes straight, sometimes arched, sometimes 
entire, sometimes lobate, emarginated, or denticulated. It 
also varies in extent. 
The body, at its lower face, is pretty constantly divided 
into transverse segments, but the upper is very often formed 
of a single piece called testa or carapace , like the tortoises. 
This vast buckler covers the body of the crabs altogether 
