4 THE ENTOMOSTRACA OF 



necessarily meet with considerable difficulty in dealing with fossil carapaces referable 

 to such genera. Thus we cannot be satisfactorily guided in our determination of fossil 

 Cyprides and Candona except by the identification of fossil with known recent forms 

 of carapace ; and, were it not that several such identifications are readily made (many 

 of the recent species having existed in the pleistocene period), the general term 

 " Cypris " might have been conveniently applied (with but little zoological licence, 

 owing to the close alliance of Cypris and Candona) to the Cypris-like carapaces from 

 fresh-water deposits. Where, however, marked differences of structure occur among 

 fossil carapaces of doubtful relationship, we may readily, for the sake of convenience, 

 group the several varieties of form under sub-generic appellations, without hazarding a 

 decision as to their exact zoological value. 



Tribe — Ostracoda, Latreille} 



Cyproides, Milne Edwards. 

 Cypmdacea, Dana. 

 Cyproidea, Dana. 



Animal enclosed in a bivalved carapace (which presents some modifications of form 

 and structure according to the gender of the animal). The two valves of the carapace 

 are united along the back by a membrane, with their edges either simply in contact, 

 or more or less closely fitting to each other by means of ridges and furrows, or toothed 

 hinges : the other marginal edges are either trenchant and provided with internal 

 narrow lamelliform plates — in which case, when the valves are closed, the edges of the 

 smaller valve lie within those of the other ; or they are thickened, and fit against each 

 other with grooved and flanged contact-surfaces. The valves are closed together by 

 the transverse muscle of the animal ; the place of the attachment of this muscle 2 is 

 indicated on the interior of each valve by a sub-central tubercle (in Cytheretta), — by a 

 sub-central shallow pit, — or by a small group of translucent spots, — or a combination 

 of spots and pit. The posterior, and sometimes the anterior jaws are branchiferous. 

 There are two or three pairs of feet, and two pairs of antennae. Some of the Ostracoda 

 have a single (coalesced) eye ; and others have two distinct eyes. 



1 See also 'Nat. Hist. Brit. Entom.,' p. 138 ; and ' Monog. Cret. Entom.,' p. 7. 



2 We are indebted to M. Zenker for a clear exposition of the relation of the transverse muscle of the 

 animal to the "lucid spots" on the carapace-valves. See his Memoir in the 'Archiv fiir Naturgeschichte,' 

 for 1854 The existence of the muscle and its place of attachment to the interior of the valves in Estheria 

 and Cypridina have been pointed out elsewhere, as mentioned in my paper on Leperditia, ' Annals and 

 Mag. Nat. Hist.,' Feb. 1856, p. 97. I much regret that I was not acquainted with M. Zenker's paper when 

 I wrote on Leperditia. 



