342 THE CANADIAN NATURALIST. [Sept. 



faint punctatioD and delicate setae, and rarely thickened on the 

 hinge-margins. The Cytheridce, on the other hand, though often 

 smooth, have frequently thick and highly ornamented valves, 

 coarsely or neatly pitted, sculptured with fret-work (more or less 

 reticulate), or bristling with spines and spikes. Either ovate or 

 oblong in many shapes, they have usually thick hinge-margins, 

 with furrows and sockets for bars and teeth. The other families 

 mentioned have smooth valves; those of Cypridina are large, 

 thick, and convex, mostly round or oval, and are marked with an 

 antero-ventral notch. Conchoecia has an oblong, and Polycope a 

 subspherical shell ; both thin. CythereJla has oblong, com- 

 pressed, thick valves, usually smooth, one fitting into the other, 

 somewhat like the lid of a wooden snuff-box. 



Of the Ostracoda very many are found fossil, such as belonged 

 to fresh waters, to brackish waters, and to the sea, in great 

 variety. Miinster, Roemer, Reuss, De Koninck, Bosquet, 

 Bornemann, and others, have described many species from the 

 strata of Germany, France, Belgium, &c. ; and at home McCoy 

 Salter, Kirby, Holl, G. S. Brady, and myself, are among those 

 who have treated of such as have been met with in the British 

 Isles; but a large number still remained undescribed. 



Amongst the fossil specimens are several that cannot be readily 

 co-ordinated with the groupings made out of the existing forms, 

 as may be expected both by the naturalists who are accustomed 

 to look on the existing races as successional representatives of 

 older forms, and by those who may regard successive fauna as 

 creational replacements. 



Among such fossil forms are many from the older (" Palaeo- 

 zoic") strata; but even for these existing representatives 

 occasionally turn up, such as Brady's Heterodesmus, lately 

 brought from the Japanese seas, which has apparently a close 

 afiinity with M 'Coy's Entomoconclms of the Mountain-limestone. 

 Some, irdeed, of the old forms are scarcely distinguishable, as 

 far as the valves are concerned, from their modern representatives ; 

 for instance, Cypridina primceva (M'Coy, sp.) of the same old 

 limestone, and its associates Cyprella and CyprideUa, present in 

 the various valves of their multiform species gradations among 

 thtmselves, and an easy passage into Cypridina itself. Others 

 among the ancient faunae possess two or more of the characteristics 

 thut are now divided amongst the several members of a group ; 

 thus the carapace of the Ltperditia of the Silurian period has 



