KNOWN SPECIES OF MARINE OSTRACODA. 363 



1. JoNESiA SIMPLEX, Norvion. (PI. LVII. fig. 11, a-e.) 



Cyihere simplex, Norman, Nat. Hist. Trans. Northumberland and Durham, vol. i. p. I7j pl- 5. 



figs. 1-4. 



Carapace compressed, elongated, rounded and narrowed in front, acuminate behind. 

 Dorsal margin straight ; ventral margin bulging considerably behind ; the two margins are 

 parallel for the greater part of their length, but converge suddenly and equally behind, 

 forming an acuminate extremity. Anterior extremity narrowed, somewhat obliquely 

 rounded. Viewed from above, the carapace is compressed, oblong oval, tapering at 

 each extremity, subacute in front, pointed behind. Und view broadly ovate. Lucid 

 spots about six in number; each spot linear-oblong and slightly curved, arranged in a 

 parallel series, those in the middle being the longest, thus forming an oval patch placed 

 in an oblique direction across the central portion of the shell. Surface smooth. 



Length -^ in. (r27 mm.). 



Hab. Hunde Islands (Dr. P. C. Sutherland's dr edgings). Shetland, Dogger Bank, and 

 Holy Island (Northumberland). Isle of Bute {Mr. D. Robertson). 



This species was very recently (1865) described by Mr. Norman from specimens 

 taken on the Dogger Bank. The perfectly simple character of the hinge-joint does not 

 allow of its being classed under any of the established genera ; and as it, in common 

 with some other species, possesses further distinctive characters, I here propose for their 

 reception the genus Jonesia, named after Professor T. Rupert Jones, whose valuable 

 labours amongst the fossil Entomostraca need no further comment. In addition to the 

 present species, Cythere contorta, Norman, and C variabilis, Baird, may be noted as 

 coming under the genus Jonesia. 



J. simplex is an exceedingly well marked species, and apparently very constant in its 

 characters, there being little or no difference observable between the specimens from 

 the various localities mentioned above. I have also seen fossil specimens collected by 

 Mr. D. Robertson from the glacial clay of the Clyde district, which are in no respect 

 distinguishable from the recent ones. The species figured by M. Bosquet (Crustaces 

 Fossiles de Limbourg) as Cytheridea harrisiana, Jones, is either identical with, or very 

 nearly allied to, the present species. The true Bairdia harrisiana, of which Mr. Jones 

 has kindly allowed me to examine the type specimens, is an entirely different thing. 



Genus Bairdia, M'Coy. 

 Animal a Cythere (i). Carapace varying from a broadly triangular form with rounded 

 or obtuse extremities, to a narrow, elongate, subtriangular form with somewhat acute 

 extremities. Surface quite smooth, finely punctate, or occasionally setiferous ; no 

 central tubercle. Lucid spots mostly well marked. The right valve is much the smaller 

 of the two, and its edge lies within, and on the dorsal margin is overlapped by, that of 

 the left. The dorsal edge of the right valve is quite simple. Ventral margin incurved. 



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