Frederick Chaio'^nan 



Leperditia shearsbii, sp. nov. (Plate I.). 



Be^cription. — Carapace elongate, sub-oval. Eight valve larger, 

 and with the ventral overlap well-marked. Seen from the side, 

 dorsal line straight, ventral margin evenly curved ; narrowly 

 rounded in front and incurving at a sharp angle to the antero- 

 dorsal angle ; widely rounded behind and meeting the 

 dorsal border with little or no angularity, differing in this 

 respect from the allied L. marginaia. Keyserling sp.^ Central 

 tubercle situated in the middle of a large, well-defined pro- 

 minence, and somewhat anterior in position. In front of this 

 tumid area the surface of the valve is strongly compressed, and 

 this is extended, as a narrow marginal flange, more or less all 

 round the caraj^ace. Casts of this ostracod show the marginal 

 compression more uniformly. This latter feature was noticed 

 by Keyserling, especially in his (?) adult or large example, and 

 was ascribed to the presence of an inverted ventral plate. Some 

 of the casts in the present series also support the idea of an 

 internal flange. Behind the central tubercle the surface of the 

 valve slopes, at first rather rapidly, and then gradually, to with- 

 in the area of the posterior third. The lucid or muscle spot is 

 best seen on the interior of the valves, appearing as a circidar 

 depression marked by a network of fine polygonal grooves with 

 a general radial arrangement. Anterior tul)ercle (eye-spot) 

 small, round and always conspicuous ; situated closer to the 

 antero-dorsal angle than in L. haJfliica, His. sp., and more 

 exactly in the position shown by L. manjinaia. The structure 

 of the valves is clearly brought out in weathered examples, and 

 the coarse pittings and radial grooving in proximity to tlif 

 central tubercle is then well seen. 

 M cnsinu'inexts (in millimetres). — 



1 " dipridina inari/inata," Keyscrlinif. Wisscnscliaftliche lieobaehtuiigen auf < 

 lleise in das Petschora-Land (UeoiJfnosHsclK' r.(.oliac'htuni;on), 184(5, p. 288, pi. xi., f. 10. 



