ESTHERIA OVATA. • 99 



The specimens of shale have the following characters : 



1. Hard, black shale (sometimes breaking up rhomboidally), fine-grained and micaceous, 

 with shining, black, filmy carapace-valves of E. ovata on the planes of bedding. One 

 specimen has the large form of carapace on one plane, and small, thickly striated indi- 

 viduals on another. 



2. Hard, black shale, like the above, with a zone of CypridcB, and with an individual 

 having the narroio form of E. ovata. 



3. Hard, black shale, granular with CypridcB, being almost entirely made up of these 

 little Entomostracans ; containing also Coprolites (of Saurians ?), and shining, black, filmy, 

 crumpled valves of E. ovata on the bed- planes. 



4. Hard, dark-grey shale (weathering rusty on the planes of bedding), containing small 

 individuals of E. ovata^ finely striated by their numerous, crowded ridges ; those on one 

 plane are almost squeezed away, those on the other retain black remains of their carapaces. 



5. Hard, dark-grey shale. Three thin bands of the dark, hornlike carapaces of ^. ovata 

 crop out on a sloping edge (weathering olive-coloured) ; besides the crowded layers, frag- 

 ments of valves are scattered between. Though apparently well preserved, these carapaces 

 show no good traces of sculpturing or structure. 



6. A similar shale, bearing a largish individual, with the narrow outline. 



7 and 8. Purple-grey shale (weathering ferruginous), and greenish-grey hard shale 

 (weathering Hght olive-green), containing a few of the smaller individuals of E. ovata, with 

 crow'ded ridges, on the bed-planes. 



9. Green shale, with Estheria similar to those in Nos. 7 and 8, but showing the 

 vertical bar-ornament figured in PI. II, fig. 37. An important link is here supplied 

 between these small EstJieria and the larger form of E. ovata, theu' relatively small size and 

 the crowding of their ridges alone remaining as distinctions. If living under disadvanta- 

 geous circumstances, a usually large carapace might be stunted in growth, and its periodical 

 peripheral additions would be small ; producing features such as we have in this case. 



In his ' Hist, des Progres de la Geologie,' vol. viii, 1860, M. le Vicomte d'Archiac has embodied all the 

 information down to 1859 respecting the Lower Mesozoic sandstones and shales of Massachusetts, Con- 

 necticut, New Jersey, Virginia, &c., under the heading " Formation Triasique," pp. 609 — 633 ; and here I 

 may supply the references to the same valuable work, that I inadvertently omitted when treating of Estheria 

 minuta. The Triassic formation of Wiirtemberg and other parts of Germany are described at pp. 426 — 549 

 of the same volume (viii, 1860) ; those of Alsace, at pp. 134 — 149 ; and those of England at pp. 16 — 50 ; 

 and the strata of Rhone Hill, Tyrone, whence E. Portlochii was derived, are treated of at p. 12. 



M. d'Archiac, in speaking of the Triassic period, in his masterly resum.6 of all that had been done 

 towards its elucidation (1860), remarks that, of the several geological formations, the Triassic is one of 

 the most curious to study — one of those which most strongly interests the naturalist, as much by the 

 variety of the inorganic phenomena connected with its origin as by the singular distribution of organized 

 beings which then peopled the earth. I must here express a hope that in the study of the history and 

 relations of these most interesting deposits some aid will be found in the foregoing pages, treating of 

 Estheria minuta of the true Trias, of its variety Brodieana in the Rhsetic beds, and of the Lower Mesozoic 

 Estherice of India and North America. 



