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 pi'ovided 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 cervus, 

 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, VA'hich 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 or 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 altogethe;. 



