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



Cytherideis, Jones. 



Cytlierideis, Jones, Post^Tert. Entom., 1856 j Brady, Monog. Eeoent Brit. Ostrac, 1868; 

 Brady, Crosskey, and Eobertson, Post-Tertiary Entom., 1874. 



Shell elongated, depressed in front, hinge-margins nearly simple ; surface smooth, 

 slightly punctate or grooved ; right valve overlapping the left in the middle of the 

 ventral surface. Anterior antennse jfive-jointed, slender, sparingly and shortly setiferous ; 

 last three joints short, and bearing six tumid setae ; penultimate and antepenultimate 

 joints, each with a single apical seta. Mandibles slender, curved, divided at the apex 

 into about four very small indistinct teeth ; palp four-jointed, bearing on the lower 

 margin of the first joint a conical tooth-like process ; third joint set along its entire 

 length with a comb-like series of straight equal setae, and bearing one large branchial 

 seta ; in other respects like Cythei^e. First segment of the maxillae much stouter and 

 larger than the rest, bearing a large branchial plate. The first pair of feet bear on 

 the basal joint a large and stout ciliated process. 



The animals belonging to the restricted genus Cytherideis are sufiiciently well 

 characterised both as to shell-structure and internal anatomy : only one species, however, 

 the British Cytherideis subulata, has yet been submitted to any anatomical investigation,^ 

 and this by no means a complete one. A few details are here added to the generic 

 description from further dissections of fresh specimens which I have, fortunately, had the 

 opportunity of making, but more yet remains to be done. The Challenger specimens 

 are very few, and seem to be all empty shells. 



The genus is widely distributed, species having been described from the British Seas, 

 the Mediterranean, the Gulf of St Lawrence, and the Atlantic, in addition to those 

 noticed in the present memoir. It is probable, too, that not a few fossil species described 

 by various palaeontologists may belong here. The forms originally referred to Cytherideis 

 by Professor T. Eupert Jones belong evidently to several distinct genera.^ 



1 Cytherideis Icevata, n. sp. (PI. VI. fig. 5, a-d, and PL XXXV. fig. 6, a-d). 



Carapace elongated, compressed, cylindrical ; seen from the side, oblong, ecj^ual in 

 height throughout, extremities rather oblique and only slightly rounded ; dorsal and 

 ventral margins quite straight and jDarallel, height rather more than one-third of the 

 length ; seen from above, somewhat club-shaped, tapering a little toward the front, width 

 greatest behind the middle, and equal to one-third of the length, broadly jDointed in 

 front, rounded off" behind ; end view neaidy circular ; surface of the shell perfectly smooth. 

 Length l-32d of an inch (775 mm.). 



1 See Brady and Robertson on the Distribution of the British Ostracoda in Ann. and Mag. Nat. Kist., ser. 4, 

 vol. ix. (1872). 



2 The name Cytherideis nana given in previous pages of this Eeport (pp. 11, 23) should have been erased. It refers 

 to specimens whose characters are not distinct enough to be made the basis of a new species. 



J 



