208 BRITISH ENTOMOSTRACA. 



former being the female and the latter the male ; and it 

 was these two different species that he had observed, as 

 he imagined, in the act of copulation. 



Tilesius and others have doubted whether the long 

 filaments attached to the posterior extremity of the thorax 

 were really ovaries. This is now clearly ascertained to 

 be the fact. They contain a great number of eggs, which 

 are round, and disposed in one single row, and even 

 young females are found, as is the case with other Ento- 

 mostraca, to possess external ovaries filled with eggs. 

 The young, when first hatched, are very different in ap- 

 pearance to the adult. In form they resemble closely the 

 young of the Cyclopidae, and, like them, undergo a series 

 of changes of skin, or moultings, before they assume the 

 completely-developed form of the parent animal. 



This family contains four British genera Caligus, 

 Lepeoptheirus, Chalimus, and Trebius. 



1. CALIGUS. Fourth pair of feet slender, of only one 

 branch, and serving the animal for walking. A pair of 

 small Innnles or sucking-discs on the lower surface of the 

 frontal plates. 



2. LEPEOPTHEIRUS. Fourth pair of feet as in Caligus. 

 Frontal plates destitute of the kmules or small sucking- 

 discs. 



3. CHALIMUS. Feet as in two preceding genera. 

 Frontal plate provided with a long and slender appendage 

 adapted for prehension, arising from the centre of its an- 

 terior surface. 



4. TREBIUS. Fourth pair of feet slender, and divided 

 into two branches, adapted for swimming. No lunules 

 or sucking-discs on frontal plates. 



