98 FOSSIL ESTHERLE. 



Habitat of Estheria ovata. — The fossil Estheria of North America, as far as I can 

 learn, have no marine associates (omitting the Fishes, for reasons already given), except 

 the little Myacites Pennsylvania^ and another, which are sufficiently obscure to be left 

 unregarded. The Cyprida associated with the Estheria at Richmond and elsewhere are 

 like our recent Can dona, and may well be supposed to have lived in fresh water. (See 

 Appendix.) The long, narrow areas within which the Estherian and carbonaceous shales of 

 the Atlantic slope were deposited may be regarded as having probably been favorable for 

 the development of freshwater and brackish lagoons, rather than for sea-creeks freely 

 open to the ocean (Rogers). 



There is evidence of the presence of salt in some of the sandstones forming part of these 

 Lower Mesozoic series of coal-bearing sandstones wid shales. But these saline sand- 

 stones are above and below the zones of Estheria (according to Emmons), with con- 

 siderable thicknesses of beds intervening (see above, page 90). 



Estheria ovata from Phaznixville, Pennsylvania. — The collection of Estherian shales 

 forwarded from Pennsylvania in May last, by Mr. C. M. Wheatley, in courteous compliance 

 with my request to be supplied with some good material fortius Monograph from the 

 tunnel near Phcenixville, comprises a large number of specimens of black, grey, purple, 

 and green shales, often crowded with Estheria ; but the carapaces are rarely in a sufficiently 

 good state of preservation to yield the desired information respecting their shape and 

 ornament, far less their structure. Besides the common broadly ovate form of carapace- 

 valve, such as appears to be characteristic of E. ovata (see PL II, figs. 26 — 28), and many 

 individuals of smaller size and with thickly crowded ridges, I find among Mr. Wheatley's 

 specimens a few of a narrower form, somewhat resembling the Indian specimen figured in 

 PI. II, fig. 16. These narrower and longer carapaces probably differ from the others 

 merely as individuals, and can scarcely be regarded as indicating a variety, certainly not a 

 distinct species. Indeed their shape may be due to oblique pressure, or to the imperfect 

 exposure of the margins, in these hardened and much crushed shales. Such as these 

 have, in all probability, been the foundation of Prof. Emmons's E. multicostata and E. 

 ovalis, above referred to (pp. 86, 87). 



The sizes of different specimens of Estheria from Phcenixville are as follows : 



Broad forms. Narrow forms. 



Height ^j inch. 1 f-^ inch ^ inch ^ inch. fa inch. 2 



L<?"gth i „ H » tV » M » H •> 



1 These small individuals are thickly striated with their numerous fine ridges, and appear to me to 

 differ from the larger individuals in having lived under conditions less favorable to their growth. 



'-' The individual here measured is possibly somewhat imperfect on the ventral edge, and may therefore 

 have been a little higher (broader) originally. 



