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



setse ; posterior antennae five or six-jointed, the first joint bearing at its base a bisetose 

 tubercle, fourth and fifth joints elongated and slender, last joint very short, and 

 terminating in two or three curved claws (fig. 2, b) ; mandibes (fig. 2, c) large, bearing six 

 or seven strong curved teeth at the dilated extremity ; palp robust, four-jointed, and 

 provided with a trisetose branchial appendage, which is attached to the basal joint. 

 One pair of jaws only (fig. 2, d), divided into three or four narrow subequal and seti- 

 ferous branches, and having a large branchial plate, which is divided into two parts by 

 a distinct constriction, the basal portion bearing six, the upper dilated and ovate portion 

 about twenty-four, long ciliated filaments. Three pairs of feet, all of similar structure, 

 directed forwards and protuding from the shell, four-jointed, and terminating in a long- 

 claw, the first pair having attached to its basal joint a large ovate, branchial lamina, 

 which, like that of the maxilla, is divided into two portions, and fringed with numerous 

 plumose filaments (fig. 2, e). Postabdominal rami (PI. III. fig. 3, e, and. PL V. fig. 2, g) 

 well developed, and of moderate length, bearing several lateral setse, and two long, 

 curved apical claws, the larger of which is (at any rate, sometimes) pectinated towards 

 the apex. Copulative organs of the male (PL III. fig. 3, a) complex in structure, and 

 not unlike those of many Cytheridce ; no spermatic glands have been noticed. The 

 animal crawls slowly about amongst the mud. 



This is a widely dispersed genus, attaining, apparently, its greatest development in 

 the tropical and southern seas, in dredgings from which regions the number of specimens 

 of BairdicB not unfrequently exceeds that of aU the other Ostracoda together ; the 

 individuals, however, though numerous, are usually found to belong in each gathering 

 to one, or at most two, predominant species. 



The anatomy of the genus has been pretty well made out by G. 0. Sars,^ from an 

 examination of the European species, Bairdia comiiilanata, Brady. The structure of this 

 animal agrees in all essential respects witli that of Bairdia villosa, a new species of which 

 several perfect examples occurred in the Challenger dredgings from Kerguelen Island, 

 and which I have been able to dissect and figure with tolerable completeness. The 

 most important generic characters, — apart from the form of the shell, the peculiarities of 

 which have long been recognised, — reside in the absence of the second maxilla, the very 

 small trisetose branchial appendage of the mandible, and the presence of a iDranchial 

 appendage to the first foot, of which, unlike the typical Cypridce, there are three pairs. 

 G. 0. Sars has, with his usual accuracy and acuteness, pointed out that this genus con- 

 stitutes a very interesting link between the two families Cypridce and Cytheridce, 

 agreeing with the first-named family in its perfectly developed postabdominal rami, and 

 with the last in having three pairs of legs, the first of which, however, answers to the 

 second maxilla of the typical Cypridce, and has attached to its base a well-developed 



' Undersogelser over Hardangerfjordens Fauna, I. Crustacea, af G. 0. Sars (Videnskabs. — Selskabets Forhand- 

 linger, p. 246, 1871). 



