COMPARISON OF HALOCYPRIDIDAE AND CYPRIDINIDAE 323 



In many members of this genus it is as broad as it is long and its longitudinal axis slopes upward. 

 In Conchoecia it is elongate and extends forward. The orientation of the body of Conchoecia is similar 

 to that of the Podocopa and it is possible that this is more primitive. It is, however, suggested that 

 the orientation of the body and arrangement of the antenna and antennal notch is partly adapted to 

 differences in the mode of swimming in the two groups. As has been mentioned when considering 



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Fig. 14. Diagrams comparing A, C. borealis antipoda, and B, Cypridina (Macrocypridind) castanea. a v antennule; a 2 , ant- 

 tenna; f.o, frontal organ; lb, labrum; mn, mandible; mx v maxillule; mx 2 , maxilla; mx 2 v, vibratory plate of maxilla; tr v first 

 trunk limb; tr x v, vibratory plate of first trunk limb; tr 2 , second trunk limb. 



the function of the antenna, the swimming action in Conchoecia is a forward propulsive stroke with 

 only a small downward component, associated with the light, boat-shaped carapace. In the Cypri- 

 dinidae, though there is a forward propulsive stroke (as mentioned by Skogsberg (1920)) the greater 

 downward component is associated with the heavy, often rounded carapace. Even in those Cypri- 

 dinidae such as Cyclindroleberis which have an elongate carapace, the body and antennal shaft have 

 a marked upward slope anteriorly. It is interesting that in the genus Halocypris where the carapace 

 is heavy and rounded rather like that of a typical cypridinid, the orientation of the body and antennal 

 shaft also is more like that of a cypridinid ; and the antennal notch is also more shallow. 



The other interesting comparison is the adaptation of the appendages for feeding. Graham Cannon 



