124 A Synopsis of the Recent British Ostracoda. 



Cytheeura, G. 0. Sars. — Upper antennae shortly setose, 

 six-jointed; lower, five-jointed, terminal claws very short. 

 Feet small, the terminal claws short and curved. Male copu- 

 lative organs very complex, provided with several irregular 

 processes and a very long spirally convoluted tube. Yalves 

 unequal and dissimilar in form, the right overlapping on the 

 dorsal margin ; produced into a more or less prominent beak 

 behind; surface smooth or variously sculptured, mostly 

 marked with a central areola of darker colour than the rest of 

 the shell. 



0. nigrescens (Baird), angulata, Brady; striata, G. 0. Sars; 

 lineata, Brady; cuneata, Brady; Sarsii, Brady; similis, G. 0. 

 Sars ; undata, G. O. Sars ; jproducta, Brady ; affinis, G. 0. 

 Sars; gibba (Miiller) ; Bobertsoni, Brady; comuta, Brady; 

 acuticostata, G. 0. Sars ; clathrata, G. 0. Sars ; cellulosa 

 (Norman) . 



The members of this genus are the most minute, speaking 

 generally, of all the Cytheridae, and the specific differences are 

 not always very clear; more extended observation will, 

 doubtless, reveal many more species. Those now known 

 inhabit chiefly deep water ; but G. nigrescens, and occasionally 

 some others, are to be found in tidal pools. Several species are 

 found fossil in the glacial clays. The most striking peculiarity 

 of the genus is the production of the shell into a prominent 

 beak or rostrum behind : the surface of the shell is often irre- 

 gularly waved or ribbed. 



Cytheropteeon, G. 0. Sars. — Upper antennae five-jointed, 

 shortly setose, penultimate joint elongated. Feet long and 

 slender, abdomen ending in a long, narrow process. Male 

 copulative organs armed behind with three spmiform processes, 

 one of which is trifurcate. Eyes wanting. Valves unequal, 

 the right overlapping above, produced towards the ventral 

 margin into a broad lateral ala, and forming behind an obtuse 

 beak. Surface marked with shallow round or angular depres- 

 sions, or with transverse ribs and furrows. 



G. subcircinatum, G. 0. Sars ; latissimum (Norman) ; nodo- 

 sum, Brady ; punctatum, Brady ; (?) multiforum (Norman). 



A genus well characterized by the strongly projecting 

 lateral alae, and great tumidity, in which, however, some spe- 

 cies of the following genus very closely resemble it : — 



Bythocytheee, G. 0. Sars. — Upper antennas seven-jointed, 

 second joint very thick, and having a single seta on each 

 margin ; the other joints much narrower, forming a slender 

 setose lash. Mandibles constricted above the distal extremity, 

 and bearing a well-developed branchial plate. Branchial plate 

 of second maxilla large, numerously ciliated, the four lower 

 cilia deflexed. Feet elongated ; basal joint of the first pair 



