Rupert Jones, on Bivalved Entomostraca. 49 



Entomostraca are sometimes associated in the shells of ]\Iol- 

 luscs. Thus Mr. J. W. Kirkby says (' Trans. Tyneside Nat. 

 Field-Club,' vol. iv, 1859),'" The convex valve of a Conchifer 

 appears to have been a popular place of resort with the 

 Bairdia, for out of one I procured some dozens of indi- 

 viduals." 



The rapid increase of some kinds of Entomostraca, and 

 the tenacity of life possessed by the eggs, are circumstances 

 that have attracted the attention of naturalists. The almost 

 sudden appearance of Apus and of Estheria in great numbers 

 in ditches, and even in cart-ruts, after heavy summer rains, 

 in Germany and France, have been particularly noted. Here 

 allusion need be made to these facts only to remind the reader 

 that the dried mud of ponds will nearly always be found to 

 contain the still vital eggs of various species of Entomostraca ; 

 and if small portions be sent home from abroad, and placed in 

 pure water, the species belonging to the original pond may be 

 produced under the eye of the naturalist and properly re- 

 corded. Thus, Mr. Henry Denny and Dr. Baird had the 

 pleasure of raising in England, from dried mud sent by Dr. 

 Atkinson from Jerusalem, several species of Entomostraca 

 new to science. (See ^Ann. Nat. Hist.' for October, 1859, 

 and September, 1861. 



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

 or shallow, running or still, — jjo^^sssing strong powers of 

 vitality and reproduction, and furnished with relatively 

 hard or tough coverings, calcareous or corneo-calcareous in 

 substance, these minute but innumerable Entomostraca have 

 left their valves, either as the exuviae of periodical castings, 

 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 

 specimens 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. Cypridina is well represented in these old 

 strata wdth Entomoconchus (before alluded to) ; Leperditia 

 lived on, with Beyrichia ; and Kirkby a flourished with Cythere 

 and Bairdia. In the fresh- water or estuarine bands Esthei'ia 

 occurs in several species, and Cypris or Candona is present 



