172 THE VOYAGE OF H.M.S. CHALLENGER. 



apex, and armed before and behind with several marginal setee or spines. Copulative 

 organs of the male very large and narrow. 



The foregoing descriptions of family and genus are borrowed from the work of G. 0. 

 Sars on the Norwegian marine Ostracoda. I have myself had no opportunity of seeing 

 the recent animal, all the specimens that have come under my notice having been empty 

 shells. It is at once apparent from the definition of the genus that we have here an 

 animal presenting a type of structure quite different from that of the preceding families, 

 in the conformation of the posterior antennae approaching the Copopoda, and in that of 

 the mandible-palps and first pair of jaws showing a likeness to the Sididse. The mode of 

 life of the animal and the manner in which the various limbs are used have not yet been 

 observed. 



Many species of fossil Cytherellce have been described, ranging from the Cretaceous 

 (doubtfuUy from the Carboniferous) to the Tertiary formations ; and judging from our 

 present knowledge of the genus, we should be disposed to say that it had attained its 

 greatest development in the Cretaceous epoch, and is perhaps now dying out. But much 

 further observation is required before this can be affirmed with certainty. 



The characters of the shells are such as to render generic reference usually a very 

 easy matter. The very unequal valves with the peripheral groove on the right side, the 

 usually distinct cuneate form of the shell, and the pinnately-arranged muscle spots, 

 are marks not to be found in any other group. Many detached valves of Cytherellce 

 were noticed in various dredgings, which it has been impossible to determine 

 specifically. 



1. Cytherella x>olita, G. S. Brady (PL XLIII. fig. 5, a-c, and PL XLIV. fig. 1, a-g). 



Cytlierella polita, Brady, Les Fonds de la Mer, p. IGl, pi. xix. figs. 5-7. 



Shell of the female, as seen from the side, subelliptical, height equal to about two- 

 thirds of the length ; extremities nearly equal and weU rounded, dorsal margin forming 

 a regular flattened arch, ventral nearly straight ; seen from above, the outline is ovate- 

 cuneate, widest near the hinder extremity, obtusely pointed in front, broadly rounded 

 behind, width equal to half the length ; end-view broadly oval. Surface of the shell 

 perfectly smooth and polished. Length, l-31st of an inch ("78 mm.). 



The form shown Id figures e-g is doubtless the male of this species, the points in 

 which it differs from figures a-d being just those which are usually characteristic of the 

 sexes. 



The type-specimens of Cytherella polita were found at Port-au-Prince, West Indies. 

 Those found in the Challenger dredgings are from the following localities : — Wellington 

 Harbour, New Zealand, in tow-net at trawl ; mouth of Rio de la Plata, 1 3 fathoms, mud 

 (Station 321). 



