142 POST-TERTIARY ENTOMOSTRACA. 



culated; usually bearing a distinct, polished, and shining tubercle over the anterior 

 hinge-joint. Hingement formed on the right valve by two terminal teeth, on the left by 

 one anterior tooth and a posterior fossa, between which there is frequently a more or 

 less strongly developed bar which is received into a corresponding furrow of the opposite 

 valve ; the teeth are in some few cases crenulated, and that of the left valve is often 

 absent. Antennae robust ; superior 5 — 6-jointed, armed on the anterior margin 

 with three long curved spines, mostly one on the third and two on the fourth joint ; 

 inferior 4-jointed, the last joint short and stout, mandibular palp 3 — 4-jointed, bearing 

 in place of a branchial appendage, a tuft of two to five setae. Eyes one or two. 

 Structure of the shell usually very dense. 



The reasons which induce us to unite the two genera Cythere and Cythereis have 

 been explained by Mr. Brady in his ' Monograph of the Recent British Ostracoda ;' but 

 as they relate entirely to the anatomy of the animal, we do not think it needful to recount 

 them here. It must be abundantly evident to all students of the group that no per- 

 manent distinctive character can be found in the shells of the two genera. 



1. Cythere pellucida, Baird. Plate III, figs. 20 — 24. 



1850. Cythere pellucida, Baird. Brit. Entom., p. 1/3, pi. xxi, fig. 7. , 



1865. — — G.O.Sars. Oversigt af Norges marineOstracoder, p. 31, 



1868. — — Brady. Monograph of recent British Ostracoda, p. 397. 



pi. xxviii, figs. 22—26, 28. 



1869. — — Brady & Robertson. Ann. and Mag. Nat. Hist., vol. iii, 



ser. 4, pi. xix, figs. 10 — 12. 



Carapace of the female, as seen from the side, narrow, elongated, almost equal in 

 height throughout, greatest height much less than half the length. Anterior extremity 

 rounded, posterior obhquely subtruncate, angular above at its junction with the dorsal 

 margin ; superior margin straight or very slightly convex ; inferior sinuated in the middle, 

 gently convex behind. Outline, as seen from above, oblong, ovate, rounded behind, 

 obtusely pointed in front, sides nearly parallel, greatest width situated in the middle and 

 equal to rather more than one third of the length. End-view nearly circular. The male is 

 narrower and more elongated. Hinge-processes distinctly developed. Surface of the 

 shell marked with more or less closely set circular pits, and with one or more curved 

 transverse furrows. 



Length, -^th of an inch. , 



The sculpture of the shell is, in this species, subject to much variation as to the 

 closeness and size of the impressions, but this appears to depend largely upon the age 

 and habitat of the specimens. The range of the species in our seas is very extensive : it 



