376 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 4, 



rarity of marine animals ; but the intervening Keuper is an exception 

 to this rule. 



Appendix. 



Note on Estheria. minuta. By T. Rupert Jones, Esq., 

 Assist. Sec. G.S. 



Not long since the Rev. W. Symonds favoured me with some well- 

 preserved specimens of this little Triassic fossil ; and, with Prof. J. 

 Quekett's kind assistance, I was enabled to see most distinctly the 

 true Crustacean character of the tissue of its valves. This confirmed 

 an opinion I had long held that this fossil is not a Mollusc, but 

 closely allied to the LimnadiUy Limnetis, and Estheria *, bivalved 

 phyllopodous Crustaceans {Entomostracd) of the present day ; and 

 indeed, as far as the carapace-valves are concerned, it well represents 

 the Estheria of Riippell and Baird f {Isaura^ Joly) • 



In the Quart. Journ. GeoL Soc. (1847) vol. iii. p. 274, Sir C. Lyell 

 figured a similar fossil from the coal-shales of Eastern Virginia, and 

 remarked that, with Mr. Morris, he doubted whether the so-called 

 *' Posidonomya" may not be a Crustacean rather than a Mollusc %. 

 Similar fossils, of different species, occur in the Devonian rocks 

 (Caithness and Orkney), Carboniferous (Northumberland), Liassic 

 (Skye and Gloucestershire), Oolitic (Scarborough), Purbeck (Dorset), 

 and Wealden (Sussex). Others are met with in the Jurassic Coal-fields 

 of North Carolina and Virginia §, and along their north-eastern ex- 

 tension, forming the so-called "New Red Sandstone" of Virginia 

 and Pennsylvania || ; in the plant-bearing sandstones of Central 

 India ^ (Nagpur and Mangali) ; and in the Triassic deposits of 

 Europe. 



Although occurring so constantly in the different geological pe- 

 riods, from the Devonian to the Wealden**, and again in the recent 

 marine and fresh waters, yet it is in the Triassic deposits of England 

 and the Continent, in the sandstones and shales of Virginia and 

 Pennsylvania, and in the plant-bearing beds of Virginia and Central 

 India, that this little bivalved Entomostracan appears to be pre- 

 eminently abundant ; so as to serve probably as a faithful index 

 of a peculiar geological horizon ff. 



In like manner, among the still lower forms of life, the Nummu- 

 lite is represented in the Silurian J J, Carboniferous, Liassic, and 



* See also above, p. 373, note. f Proe. Zool. Soc. part 17. p. 86. 



% See also Lyell's ' Manual of Geology,' 5th edit. p. 332. 



§ Lyell, loc.cit.; and W. B. Rogers, Boston Nat. Hist. Soc. Proc. v. p. 15. 



II Continuous with the Sandstones of New Jersey, and most probably with 

 those of Connecticut also : Rogers, loc. cit. 



^ Quart. Journ. Geol. Soc. vol- xi. p. 370. 



**. I have no satisfactory evidence of the presence of the genus in question in 

 the Cretaceous and Tertiary deposits. 



ft Prof. W. B. Rogers has already pointed out {loc. cit.) the probable value of 

 this little fossil in the comparison of the Mesozoic rocks of North Carolina and 

 Virginia, and of these with the so-called Triassic beds of the United States. 



XX Annals and Mag. Nat. Hist. ser. 2. vol. xv. p. 58. 



