RECENT BRITISH OSTRACODA. 



471 



teeth ; palp biarticulate, first joint stout, bearing externally a short, bisetose branchial 

 appendage, last narrow, beset with long plumose setae. Incisive portion of the firs£ pair 

 of jaws small, forming a simple setiferous lobe ; palp very large, four-jointed, two-branched, 

 second joint bearing externally a long, narrow, and obsoletely biarticulate branch, which 

 is terminated by long setae. Second pair of jaws membranaceous, three-jointed; penul- 

 timate joint bearing externally a small branch which terminates in a single seta ; furnished 

 at the base with a large branchial plate. Postabdominal plates short, posterior margin 

 shortly digitate and armed between the segments with acuminate claws. Animal swim- 

 ming actively like the Lynceidae." 



Sars thinks that there are probably several species of this genus, but he has not been 

 able accurately to examine and determine more than one. The two species here described 

 I myself know only from their external characters, the few British specimens hitherto 

 found being apparently empty shells. 



1. PoLYCOPE ORBICULARIS, G. O. Sars. (Plate XXXV. figs. 53-57.) 

 Polycope orbicularis, G. O. Sars, loc. cit. p. 122. 



Shell oii\\Q female, as seen from the side, subcircular, greatest height in the middle, 

 slightly less than the length ; anterior margin slightly narrowed and produced, posterior 

 evenly rounded, superior and inferior margins boldly arched. Outline, as seen from above, 

 ovate, tapering equally to each extremity ; greatest width in the middle, equal to more 

 than half the length. Valves finely punctate and divided by fine reticulated ribs into 

 numerous polygonal areolae. Colour pale yellow, marked with patches ("radiating 

 stripes," Sars) of a darker red colour. " Basal joint of the upper antennae longer than 

 the two others combined, densely hairy on the anterior margin, and provided with a 

 short seta, last joint ending in five long slender setse ; one branch of the lower antennai 

 eight-jointed, the last seven joints short and subequal; the other three-jointed, first joint 

 longer than the two following combined, bearing eight long partly ciliated setae. Man- 

 dibles divided at the apex into five teeth, the most external of which is much the larger ; 

 palp shorter than the mandible itself, its last joint equal in length to the basal joint 

 and bearing seven ciliated setae. Secondary branch of the anterior maxillae reaching a 

 little beyond the apex of the palp, and terminating in about eight very long and slender 

 setae. Branchial plate of the posterior maxillae narrow, elliptical, bearing sixteen ciliated 

 marginal setae. Postabdominal plates armed with six finely ciliated claws decreasing 

 gradually in length backwards ; behind them two short setae. Posterior margin of tlie 

 abdomen bearing three brushes of short hairs. Male unknown." 



Length gV ill- 



Hab. Shetland and the Minch {Rev. A. M. Norman); in oyster-oozc from Stranraer (G. S.B.); in 

 shell-sand, Roundstone (Dr. Alcock). 



There seems to be much difference in the amount of sculpturing of different specimens 

 of P. orbicularis. In adults the shell is often almost perfectly smooth, though mostly 

 bearing an obscure reticulated pattern ; a single valve from shell-sand at Boundstone 

 (represented at figs. 56 & 57) is more distinctly sculptured than any other specimen 

 that I have seen. Young specimens are punctate but not reticulated. 



