REPORT ON THE OSTRACODA. 171 



Section PLATYCOPA. 



Family Cythekellid^, G. 0. Sars. 



Valves unequal, very thick and calcareous, not notched in front. Antennae very 

 large, the anterior many -jointed and geniculated at the base ; posterior broad and 

 flattened, two-branched like the feet of the Copepoda. Mandibles very small, with a 

 large pectinato-setose palp. Three pairs of hinder limbs, scarcely pediform ; the two 

 anterior pairs branchial, the others rudimentary. Abdomen terminating in two very 

 small, narrow, and sj^iniferous laminae. Ova and embryos borne beneath the shell of the 

 female. 



Cijtherella, Jones (1849). 

 Cytherella (sub-genns), Jones, Entom. of Cretaceous Formation (1849), G. 0. Sars (1865), G. S. Brady (1865). 

 Valves elongated, flattened, thick and hard, very unequal ; the right much larger 

 than the left, overlapping throughout the whole circumference, and presenting round the 

 entire inner margin a distinct groove, into which the valve of the opposite side is 

 received. Muscle-spots arranged in a curved pinnate series on an oblong, obliquely 

 placed depression near the centre of the shell, the depression appearing internally as 

 an elevation. Spots from twelve to sixteen in number, linear oblong in shape, and 

 increasing in size toward the ventral margin. Anterior antennae very large, shortly 

 setose or spiniferous, seven-jointed, the first two joints larger than the rest, and 

 forming between them a distinct geniculation ; posterior antennse composed of a large, 

 broad, biarticulate, and geniculate basal portion, from which arise two flattened unequal 

 branches, one biarticulate, the other triarticulate, both beset with very numerous long 

 setae. Labrum large, sublobose, giving out in front a short subtriangular jorocess. 

 Mandibles very weak, strongly inflexed at the lower extremity, which is obliquely 

 truncate, and set in a pectinate manner with slender teeth ; palp large and elongated, 

 almost straight, bearing on its inner side very numerous long, pectinately-arranged 

 setae, which stretch backwards as in the feet of the Sididae. First pair of jaws bearing 

 at the base a very large branchial plate, which is beset with numerous ciliated 

 marginal setae ; incisive portion divided into three setiferous lobes ; palp very large, 

 scarcely articulated ; the posterior margin slightly lobated, inner margin pectinately 

 setose, like the mandibular palp, but smaller. Second pair of jaws membranaceous, 

 bearing, like the preceding pair, a branchial plate, but smaller and narrower ; distal 

 portion subovate, beset with a few ciliated setae, and in the male furnished with a 

 very large and strong hatchet-shaped appendage adapted for prehension. Third pair of 

 jaws, in the female, rudimentary, forming a simple setiferous lobe ; in the male, strong, 

 distinctly jointed, and subcheliform. Abdomen beset behiad with several bundles of 

 long setae for supporting the ova. Postabdominal laminae narrow, slightly dilated at the 



