CYPROIDEA. 1277 



Length, one-thirtieth of an inch. 



The antennae have a long basal portion, with the branches a little 

 shorter than this base. The body is much narrower at the junction 

 of the head and thorax than elsewhere. The eyes are enclosed 

 within a cornea beneath the shell, which admits of some motion, 

 mostly rotary. The heart is an oval organ, situated near the dorsum, 

 in the anterior portion of the thorax. The large cavity over the body 

 within the shell was empty. 



Polyphemus brevicaudis, Dana, Proc. Amer. Acad. Sci., ii. 49. 



Tribe III. CYPROIDEA. 



The Cyproidea differ from .all other Crustacea, excepting the Ler- 

 nseoids and Rotatoria, in the absence of the pairs of appendages belong- 

 ing to all the normal cephalothoracic segments posterior to the eighth, 

 that is, to the six posterior of these segments. The last two of these 

 six pairs are obsolete in all the Lophyropoda ; and in the Cyclopoidea 

 and Daphnioidea, the first four of them are natatory or foliaceous, 

 together with also another pair, next anterior in most species. The 

 pairs of appendages present in the Cyproidea, posterior to the man- 

 dibles — in number four pairs — are divided variously between the mouth 

 and legs. The modes observed are as follows : — 



1. One pair of maxillae and three pairs of legs, as in Cythere. 



2. Two pairs of maxillae and two pairs of legs, as in Oypiis, Con- 

 choecia, and Halocypris. 



3. Three pairs of maxillae and one pair of legs, as in Cypridina. 

 The outer pair of maxillae may be called maxillipeds, yet they are 

 more like maxillae in form. 



The posterior legs may be true feet, as in Cythere, Conchoecia, and 

 Halocypris, or slender organs fitted for action in the ovarian cavity, 

 as in Cypris and Cypridina. 



On Plate 90, we have arranged the several appendages of the difle- 



320 



