CLASSIFICATION 109 



oars, the valves of the shells being excavated to admit of free 

 movements. There are two pairs of maxillae ; the succeeding 

 limbs differ in the two families. In the Cypridinidae, e.g. Aster ope 

 (Fig. 75), the first leg (T) is lamelliforrn and is used as an 

 accessory maxilla, while the second leg (T 7 ) is turned upwards 

 into the shell as a cleaning organ. In the Halocypridae the first 

 leg is pediform, and differs in the two sexes, while the second 

 leg is rudimentary and points backwards. In Asterope peculiar 

 branchial organs (G) are present on the back. Both families 

 possess a heart ; the Halocypridae are blind, while the Cyprid- 

 inidae possess eyes. 



The Polycopidae and Cytherellidae are curious marine 

 families of a pelagic habit, with biramous second antennae well 

 adapted for swimming, and very broad. The first maxilla in the 

 Polycopidae is also employed in swimming, while the second is 

 modified into a branchial organ ; the maxillae of the Cytherellidae 

 are more normal in structure, but both carry branchial lamellae. 

 The posterior limbs are altogether absent in Polycopidae, and in 

 the Cytherellidae are only represented by the copulatory organs 

 of the male. 



