4 POSSIL ESTHERIiE. 



the so-called " New Red Sandstone " of Pennsylvania ;' and in the plant-bearing sandstones 

 of India (Mangali, Panchet, and Kotah) ; and in beds of undetermined age (probably 

 Tertiary) in Siberia and South America. 



Although occurring so constantly in the different geological periods, from the Devo- 

 nian to the Weal den/ and again in some Tertiary beds and in the recent fresh waters, 

 yet it is in the Rhsetic and Triassic deposits of Britain and the Continent, and the 

 sandstones and bituminous shales of Pennsylvania, Virginia, and Carolina, and in the 

 plant-bearing beds of 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.^ 



In like manner, among the still lower forms of life, the Nummulite is represented in 

 the Carboniferous, Liassic, Oolitic, and Cretaceous rocks, and exists also at the present 

 day ; but it particularly distinguished one epoch (the Tertiary) by a surprising fecundity 

 and a temporary profusion of individuals. 



The occurrence of a fossil Estheria in the Upper Sandstone and Shale of the Scar- 

 borough district {E. concentrica, Bean,^ sp.) is of considerable interest, as indicative of the 

 association of this crustacean genus with the Jurassic flora in England, as it is with a 

 Jurassic-like flora in India and North America. 



In India a Triassic Labyrinthodont reptile {BracJdops laticeps ^) is found in the same 

 strata as yield the Estheria at Mangali, possibly contemporaneous, or nearly so, with those 

 containing plants at Nagpur ; near Panchet also, in north-eastern India, Estheria occurs in 

 equivalent beds, with Dicynodont and Labyrinthodont remains ; and in Pennsylvania 

 reptilian remains ® occur with the so-called " Posidonomya ; " in North America, indeed, 

 the evidence seems to point to a contemporaneity of the coal- and plant-beds of Carolina 

 and Virginia, the shales and sandstones of Pennsylvania and New Jersey, the foot-marked 

 sandstones of Connecticut, and the Upper Red Sandstone of Nova Scotia and Prince 

 Edward's Island, which is also reptiliferous ; ^ and it is evident that in the Virginian and 

 Pennsylvanian shales the minute crustaceans under notice are important fossils. The 

 fossil plants of India and of Virginia and Carolina having a Jurassic facies, like those of 

 the Venetian Alps and Scarborough, it will be interesting, as further evidences turn up, 

 to see how far we are to regard the Triassic or the Jurassic element as preponderating, or 



1 Continuous with the sandstones of New Jersey, and most probably with those of Connecticut also. 



^ I have no satisfactory evidence of the presence of the genus in question in the Cretaceous deposits. 



^ Prof. W. B. Rogers has already pointed out (' Boston Nat. Hist. Soc. Proc' v, p. 15, &c.) 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. 



* 'Mag. Nat. Hist.,' vol. ix, p. 376. 



5 'Quart. Journ. Geol. Soc.,' vol. ix, pp. 37 and 371. 



^ Lea on Clepsysaurus Pennsylvanicus, 'Journ. Acad. N. Sc. Philad.,' n. s., vol. ii, p. 185 ; and on 

 Centemodon sulcatus, 'Proc. Acad. N. Sc. Philad.,' n. s., vol. viii, p. 377. 



7 Leidy on Bathygnathus borealis, ' Journ. Acad. N. Sc. Philad.,' n. s., vol. ii, p. 327. 



