REPORT ON THE OSTRACODA. 47 



One specimen only of this species was found in material dredged in 18 fathoms oft' 

 Tongatabu, South Pacific (Station 172). From Bythocyjiris reniformis it is separated by 

 the broad, very oblique, and downwardly produced anterior margin, as well as by a gene- 

 rally more elongated contour. 



[PI. XXXV. fig. 5, a-cl. a Shell seen from left side, b from above, c from below, 

 d from front. All magnified 50 diameters.] 



3. Bythocyi^ris elongata, n. sp. (PL VI. fig. 1, a-c). 



Carapace compressed, elongated ; seen from the side, subreniform, highest in the 

 middle, height equal to about half the length ; anterior extremity rounded off', posterior 

 somewhat produced, narrowed, scarcely rounded ; dorsal margin forming a flattened 

 arch, which slopes much more abruptly behind than in front ; ventral very slightly 

 sinuated in the middle ; seen from above the outline is elongate-ovate, widest in the 

 middle, and having subacuminate extremities. The valves are unequal, the right being 

 somewhat lower and more angular in outline than the left. Surface of the shell quite 

 smooth. Length, l-22d of an inch (I'l mm.). 



Only a few separated valves of this species have been noticed. It is impossible to 

 refer them even provisionally to any known species, and their true generic position is 

 also doubtful. In general appearance they seem to come nearer to BythocyjJris than to 

 any other genus. The specimens described were found in a dredging from a depth of 

 1425 fathoms, north of Tristan d'Acunha, lat. 32° 24' S., long. 13° 5' W. (Station 335). 



Bairdia, M'Coy. 



Bairdia, M'Coy, Carb. Limest. Foss. Ireland, 1844. 



Valves unequal in size, the left much the larger of the two, and overlapping the 

 right on the dorsal, and in the middle of the ventral surface ; the right valve (PI. VIII. 

 fig. 1 , e) is narrow, elongated, and angular ; its anterior margin often rather produced 

 at the lower extremity ; dorsal margin flattened in the middle, and sloping steeply 

 toward each end ; the posterior extremity produced into a more or less prominent beak ; 

 and the ventral margin more or less sinuated; the left valve (fig. l,f) is much less 

 angular in outline, dorsal margin much elevated, and very strongly arched ; ventral 

 convex ; anterior extremity broadly rounded, posterior narrower, but not beaked. 

 The shape of the shell is variable, — reniform, subtriangular or subrhomboidal ; 

 hinge simple, and without teeth ; shell-surface smooth, hirsute or slightly punctate. 

 Muscle-spots not far from the centre of the valves, and arranged usually in a 

 rosette. Eyes absent. Antennse usually robust ; the anterior pair six to eight-jointed 

 (PL V. fig. 2, a), first two joints large, the rest short, and finally joined together, "but 

 forming with a second joint, a movable hinge " (Sars), and bearing numerous long, apical 



