192 POST-TERTIARY ENTOMOSTRACA. 



lobes of the first pair of maxilla) long and narrow, " branchial plate bearing on its 

 external margin two non-ciliated setae, which are directed downwards, and arise from a 

 separate lobe." Feet small, the terminal claws short and curved. Eyes distinct. Copu- 

 lative organs of the male very complex, provided with several irregular processes and a 

 very long spirally convoluted tube. 



The species belonging to this genus are the smallest of the Cytlieridce ; they occur in 

 considerable numbers, and various species are so closely related one to the other that 

 it is often by no means easy to identify them with certainty. The species we have now 

 to describe are to a large extent identical with those now living in the British seas. 



1. Cytherura nigrescens {Baird). Plate XI, figs. 28—32 ; and Plate XII, fig. 13. 



1838. Cythere nigrescens, Baird. Mag. Zool. Bot., vol. ii, p. 143, pi. v, fig. 27. 

 1850. — — Baird. Brit. Entom., p. 1/1, pi. xxi, figs. 4, 4 a. 



1865. Cytherura — G. O. Sars. Overs. Norg. mar. Ostrac, p. 71. 



1868 — — Brady. Monog. Rec. Brit. Ostrac, p. 440, pi. xxxii, 



figs. 50 — 55 ; pi. xxxix, fig. 7. 



Carapace oi female, as seen from the side, subrhomboidal, highest in the middle, greatest 

 height equal to quite half the length ; anterior extremity rounded, posterior produced 

 above the middle into a short obtuse beak ; superior margin evenly and boldly arched, 

 inferior slightly sinuated. Outline, as seen from above, compressed, ovate, pointed at each 

 extremity, widest in the middle, width equal to rather more than one third of the length. 

 End-view broadly ovate. Surface of the shell smooth, often slightly punctate. 

 Length, -^nd of an inch. 



Distribution. Recent. — Norway, Great Britain, Ireland. 



Fossil. — England : Hopton CliflF. Scotland : nearly all the Post-tertiary beds on the 

 west, and at Drip Bridge. Ireland : New Dock at Belfast, Portrush. Norway and 

 Canada. 



2. Cytherura similis, G. 0. Sars. Plate XI, figs. IG— 18; Plate XII, fig. 16. 



1865. Cytherura similis, G. O. Sars. Overs. Norg. mar. Ostrac, p. 72. 

 1868. — — Brady. Monog. Rec. Brit. Ostrac, p. 442, pi. xxxii, 



figs. 56—59. 



Carapace, as seen from the side, subovate, highest in the middle, greatest height equal 

 to rather more than half the length ; anterior extremity rounded, posterior produced in 

 the middle, but scarcely beaked ; superior margin boldly and evenly arched, inferior nearly 



