18 FOSSIL ESTHERLE. 



is about six miles. In Caithness, as in Orkney, it is only found in the middle member 

 of the Old Red Sandstone, associated with Asterolepis, Coccosteus, Dipterm, Diplopterus, 

 and Osteolepis. 



" Of the vertical range of the Estheria it is difficult to speak, as all the localities in 

 Caithness, alluded to above, are high up in the middle member of the Old Red series : if, 

 however, quarries were opened lower down in this middle group, I venture to anticipate 

 that the Estheria would still be found, as the same mineral conditions (calcareo-argillaceous 

 flagstones, intercalated with sandstones,) persist almost from the top to the bottom of that 

 group in Caithness, accompanied by the same characteristic fauna of Fishes, their scales 

 being diffused throughout the strata in great abundance ; and, as the Estheria have often 

 been mistaken for the scales of Dijpterus, I think it probable that many of those supposed 

 scales may turn out to be the carapace-valves of the little Crustacean under notice." 

 [J. Miller, February 4, 1861.] 



The specimens of flagstone, bearing Estheria membranacea, that I have seen are 

 as follow: — 1. A black, micaceous, fine-grained flagstone, having a grey streak, and 

 weathering olive-grey; the Estherian valves numerous, pyritous, iridescent under the 

 microscope, and retaining no trace of the surface-ornament; accompanied with a coprolite- 

 looking body. 2. From Thurso East, a greenish-grey micaceous flagstone, slightly 

 calcareous ; the valves numerous, preserving their tissue, but crumpled and broken. 

 3. From Murkle Bay, greenish-grey, micaceous, calcareo-argillaceous flagstone ; the valves 

 numerous, retaining here and there portions of their surface. As Hugh Miller has already 

 observed, 1 the valves do not for the most part lie thinly and evenly scattered over the 

 bedding planes of these hard laminated mudstones, but are clustered here and there in 

 thickly set groups. 



The valves occasionally retain their substance, and are then brown, opaque, and 

 rugose ; usually, however, a thin, smooth, shining, light-brown, horn-like film is all that 

 remains. 



Though the majority of existing and fossil Estheria have more or less oviform cara- 

 paces, with the umbo situated at or near the antero-dorsal angle, yet the position of the 

 umbo at or near the centre of the dorsal line (as in E. membranacea) is not foreign to this 

 genus ; for E. Histopi, Baird (' Zool. Proceed,' 1859, p. 232, Annulosa, pi. 63, fig. 1), 

 from India has this condition; and E. concentrica, Bean, sp. (PI. Ill, figs. 13 — 17) may 

 be said to stand in the same category. 



In July, 1859, Mr. J. W. Salter showed me some specimens (from Russia) of light- 

 grey, very finely grained arenaceous clay, containing an Estheria apparently identical 

 with E. membranacea, labelled " Asmusia ynembranacea, R. Pacht ; with traces of Litu/ula 

 bicarinata, 2 Kutorga ; Kokenhusen." Dr. Pander has also favoured me with some specimens 

 from Kokenhusen. These are identical with the Estheria from Caithness. 



1 ' Cruise of the Betsy,' p. 415. 



2 Lingula bicarinata is figured and described by Kutorga, in his ' Beitrage zur Geognosie und 



