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



Xestoleberis, G. 0. Sars(1865). 



Shell smooth and polished, ornamented with small, round, distant papUlse, or rarely- 

 marked with sculptured pittings, much lower in front than behind, and in the female very- 

 tumid behind. Hinge-joint formed by a dentated projecting crest of the left, which is 

 received into an excavation of the right valve ; ventral margin of both valves incurved 

 in front of the middle, and forming on the ventral surface a central hollow ; anterior 

 antenna six-jointed, the last four joints successively decreasing in length, and bearing 

 very short, simple setae ; posterior antennae short, four-jointed, flagellum of moderate 

 length. Mandible-palp four-jointed ; branchial appendage small, and bearing only two 

 setae. Jaws as in Loxoconcha. Feet small ; post-abdominal lobes bearing two setae. 

 Eyes distinct. Ova and immature young borne within the shell of the female, 



This genus is at a glance distinguishable by the generally rounded outline, the 

 depressed and pointed front, and the rounded, tumid posterior end of the shell. It is 

 widely distributed, containing apparently a very large number of species, and occurring 

 abundantly in the seas of all parts of the world. So far, however, as we know of it 

 palaeontologically, it would seem to be a genus of comparatively recent development, the 

 only described fossil species which can be unmistakably referred to it — so far as I know 

 — being Cytherina impressa, Eeuss (a chalk-marl species extremely like in the published 

 figures to the recent European species, Xestoleberis de^oressa and awrantia) , Cytheridea 

 tutnida, Egger ( = ? Cytherina tumida, Reuss), and Bairdia glutea, Egger, the last two 

 being Miocene species. Zoologically, the most remarkable character of Xestoleberis is its 

 being viviparous ; the fry are retained within the shell of the mother until very fully de- 

 veloped : this, perhaps, may account for the great posterior expansion of the female carapace. 



1. Xestoleberis depressa, G. 0. Sars (PI. XXXI. fig. 1, ct^g). 



Xestoleberis depressa, Sars, Oversigt af Norges marine Ostracoder, p. 68, 1865. 



Xestoleberis depressa, Brady, Monog. Eecent Brit. Ostrac, Trans. Lin. Soc, 1868, p. 438, pi. 



xxvii. figs. 27-33. 

 Xestoleberis depressa, Brady, Crosskey, and Eobertson, Post-Tertiary Entomostraca, p. 190, pi. vii. 

 figs. 13-19. 

 (?) Cytherina tumida, Eeuss, Foss. Entom. Oesterr. Tert., Beckens, p. 57, pi. viii. fig. 29, 1850. 

 (?) Cutheridea tumida, Egger, Ostrak. Miocan-Schicht, Ortenburg, p. 17, pi. ii. fig. 11. 



Carapace of the female tumid; seen from the side, oblong, sub-semicircular, highest 

 near the middle, height equal to more than half the length ; subacutely pointed in front, 

 broadly rounded behind, dorsal margin boldly arched and forming one continuous curve 

 from the anterior to the posterior ends of the ventral margin, which is straight, except 

 for a slight sinuation in front of the middle. Seen from above, the outline is cordate, 

 pointed in front and broad behind, width equal to two-thirds of the length ; end view 

 depressed, broad below and boldly arched above, width greater than the height. Surface 

 of the shell smooth, iridescent, marked with numerous small circular papillae. The shell 



