346 THE CANADIAN NATURALIST. [Sept. 



several species of Eotomostraca new to science. (See ' Ann. 

 Nat. Hist.' for 1859 and September, 1861.) 



Flourishing, then, in every water-area, fresh or salt, deep or 

 shallow, running or still, — possessing strong powers of vitality 

 and reproduction, and furnished with relatively hard or tough 

 coverings, calcareous or coriieo-culcareous in substance, these 

 minute but innumerable Entomostraca have left their valves, 

 either as the exuvia of periodical castinss, or as the lasting 

 remains of hosts of animalcules buried in the tide-shifted silt or 

 the mud and sand of the freshet, to be fossilized in laminated 

 clays, hardened mud-stones, and solid rocks of limestone. 



In the extremely old "Silurian" strata we find abundant 

 sp\-iraens of Primitia, Beyrichia, Leperditia. and Entomis, 

 apparently related to the Phyllopods, and always associated 

 with marine fossils. In the " Devonian '' beds of marine origin 

 we find Entomis, &c. ; and in the fresh-water beds of the same 

 period there is an Estheria, both in Scotland and Russia. The 

 ''Carboniferous" formations next succeed, and contain a host 

 of Bivalved Entomostraca, many of them not yet described. 

 Cyprldina is well represented in these old strata with Entomo- 

 conchus (before alluded to) ; Leperditia lived on, with Beyrichia ; 

 and Kirkhya flourished with Cythere and Bairdia. In the 

 fresh-water or estuarine bands Estheria occurs in several i-pecies, 

 and Cypris or Candona is present also. The persistence of these 

 genera from so old a time to the present is what is expected of 

 such relatively low forms of life ; wide geographical extension 

 and long continuance belonging to such creatures as have not 

 been highly specialised. In the " Permian '' formations (" Mag- 

 nesian Limestone" of Durham and other strata) Bairdia, 

 Cythere a.nd Kirkbya :p\dy nn important part. In the " Trias" 

 or "New Red Sandstone" we find Estheria, where marine 

 conditions failed and fresh water had an influence, not only in 

 Europe, but in India and America. (See my ' Monograph on 

 Fossil Estheriae,' 1862.) The Entomostraca of the " Lias " 

 and the " Oolites " are not few, though not well known. In 

 the " Purbeck " and " Wealden " beds they are better known. 

 Masses of Purbeck building stone are wholly composed of the 

 valves, and some of the Weald clays split like paper along the 

 layers of shed valves of Cypridea : nor are Estherim wanting in 

 these old fresh-water beds. The " Gault " and " Chalk " are full 

 of Cythere^ Bairdia, and other allied genera, all marine. The 



