CRUSTACEA. 



281 



are often curiously branched j and the hinder extremity is usually pro- 

 duced into a sort of tail, which is seen in constant action when the 

 animal is in motion. 



This order divides into two families the Cypridoe, in which the body 

 is entirely enclosed by the shell, of which 

 the genus Cypris (fig. 122) is an example; 

 and the Dapliniadce, in which the head is 

 protruded beyond the shell. In the Poly- 

 pliemus, belonging to this group, the head, 

 which is large, is almost entirely occupied 

 by an enormous eye, giving the creature a 

 most singular appearance. 



The Monoculus is a well-known example 

 of this group. Another family, not pro- 

 vided with a shell or carapace, are called 

 Branchipodidce, from the name of the typi- 

 cal genus, Branchipus stagnalis (fig. 122), 

 an animal which is often found after heavy 

 rains in cart-ruts and other small pools. 

 Another species, the Artemia salina, in- 

 habits a still more curious situation, namely, 

 the salt-pans at Lymington, where it is usu- 

 ally found in those pans in which the evapo- 

 ration of the water has proceeded to a considerable extent. 



A few years since only a small number of the Entomostraca were 

 described. Dr. Baird, of the British Museum, has lately published a 

 valuable volume upon the British species alone. 



The Gammaridce are characterised by the large size of the foot- 

 jaws, which cover the whole mouth. The common Talitms locusta, or 

 sand-hopper, which may be met with in thousands upon the sands of 

 our shores, is a well-known example of this family. Although its 

 length is not .much more than half an inch, it can leap several inches 

 into the air, and the facility with which it escapes pursuit by burrowing 

 into the soft wet sand is truly wonderful. Another species, Gammarus 

 pulex, is found commonly in fresh water, and is scarcely inferior to its 

 marine relative in agility. 



The CorypJiium longicorne, remarkable for its long antennae, is not 

 less so for its singular habits. It is found at Rochelle, where it bur- 

 rows in the sand, and wages constant war with all other marine crea- 

 tures of moderate size that come in its way. To discover their prey 

 they beat about in the mud with their large antennae. 



fig. 122. 



I. Cypris. 2.- Cyclops-. 

 3. Branchipus stagnalis. 



