RECENT BRITISH OSTRACODA. 



421 



The excessively rugged surface of the shell would, indeed, constitute a serious impedi- 

 ment to any rapid movement through the water ; consequently we do not observe any 

 such condition of carapace in the genus Cypris, nor even in Candoua. The two or 

 three specimens on which the species was originally founded are all that have as yet 

 been observed. It may be noted that specimens of Cypris gibha sometimes assume a 

 tuber culated or spinous surface ; but never, so far as I know, to such an extent as in 

 the present species. 



Genus 3. CyTHERiDEA, Bosquet. 



Shell, as seen from the side, subtriangular or triangularly ovate, highest at the anterior 

 third ; thick and compact in structure. Surface more or less pitted, sometimes smooth 

 and papillose, or concentrically rugose. Hinge-margin of the right valve bearing a series 

 of small tubercles or crenulations, which are received into corresponding depressions of 

 the opposite (left) valve ; these tubercles are mostly disposed in two terminal groups, the 

 intervening portion of the valve-margin being plain or marked by minute tubercles on 

 the left, and corresponding fossae on the right valve. Lucid spots about four, in a trans- 

 verse row, near the centre of the valve, and two detached spots (which sometimes 

 coalesce) in front of the main group. Tipper antennae very robust, mostly five-jointed^ 

 and bearing strong spines; the last joint narrow and elongated; lower antennse four- 

 jointed ; urticating setae long and slender, biarticulate. Mandibles large and numerously 

 toothed ; palp three-jointed, and bearing a distinct branchial appendage. The right foot 

 of the first and second pairs in the male different from the rest, that of the first pair 

 very strong and prehensile ; of the second very feeble, the apical portion rudimentary 

 and destitute of a terminal claw. Eyes distinct. 



I am unable to find any good distinctive characters to separate the genus Cyprkleis 

 (Jones) from Cytheridea. G. O. Sars restricts the latter genus (apparently) to certain 

 very broad and dentate forms, which, however, do not appear to me to present any well- 

 marked generic characters : the animal is not known, but may be supposed to be, in all 

 probability, not far different from that of the typical Cytheridea {Cyprideis, Sars). It 

 may be noted that some of the species included by Sars under Cyprideis belong dis- 

 tinctly to the series included by Bosquet in his Cytheridea; and one of them {Cyprideis 

 Sairdii, Sars) is, as I believe, identical with Cytheridea papillosa, Bosquet. If the dis- 

 tinctness of the two genera be maintained, the name Cyprideis should, I think, be reserved 

 exclusively for C. torosa, which differs to some extent in its anatomy, and probably also 

 in its mode of reproduction. Many of the fossil forms described by authors as Bairdice 

 belong undoubtedly to Cytheridea. The genus is a small one ; bnt some of the species, 

 though local, occur in prodigious quantities when the conditions of existence are 

 favourable. 



1. Cytheridea elongata, Brady. (Plate XXVIII. figs. 13-16, and Plate XL. fig. 6.) 

 Cythere angustata, Baird, Brit. Entom. p. 172, tab. xxi. fig. 6. 



Atlantic type. Distribution : Recent — Great Britain, Ireland, Bay of Biscay. Fossil — Glacial deposits 

 and raised Leaches, Scotland and Ireland. 



Carapace, as seen from the side, elongate, not much higher beliiud than in froct ; 



