24 POSSIL ESTHERItE. 



favour this view. Moreover, there are smaller JEstheric^ in the Carboniferous strata, show- 

 ing their characteristic features (PI. II, figs. 39, and PL V, figs. 1 — 7) more clearly, just as 

 the small Estheria elliptica of the Wealden (PI. IV, figs. 6, 7) exhibits a sculptured 

 ornament, whilst the larger specimens have the surface obscured by thickly set striae (figs. 

 1 — 5). E. striata, also, like other Estherice, has subquadrate individuals (see p. 11). 



Estheria striata may be thus characterised : 



Carapace-valves thin, nearly oblong, but somewhat higher at the posterior third than 

 anteriorly; umbo distinct, placed forward, being situated at the antero-dorsal angle, 

 beyond which the convexity of the anterior border projects but slightly ; posterior border 

 boldly roimded, usually more or less elliptical and oblique ; ventral border gently and 

 obliquely convex. The surface of the valves presents numerous concentric wrinkles (30 

 — 50 or more), some of Avhich appear to be the raised ridges usual in Estheria, and the 

 others are due to finer intermediate striae (figs. 10, 12, and 14). The surface is frequently 

 found to be wrinkled transversely (as in figs. 1 and 14) with very delicate corrugations 

 crossing the concentric ornament, and due to mechanical causes. Coarser wrinkles, also 

 due to the crumpled state of the fossil valves, are often seen (as in fig. 12) ; the latter 

 seem to affect the inner portion of the shell, which (as we see by figs. 16 and 17) some- 

 times shows a cellular appearance analogous to the reticulate structure of crustacean shell. 

 This reticular tissue is found freely dispersed on the shale from Lammerton, over some 

 portions where but little other trace of the Estherian valve itself remains. Where the 

 boundaries of the meshes make strong lines parallel with the concentric lines of growth of 

 the shell (as in fig. 17), the fine intermediate striae of the surface would probably be 

 stronger than Mdiere the reticulation is irregular, as in fig. 16. 



Of ^. striata I have seen numerous specimens from several different localities ; namely, — 

 1 . Erom Lammerton, Berwickshire ; in bituminous shales belonging to the Mountain-lime- 

 stone series. 2. Erom the Lanarkshire coal-field (in cannel-coal). 3. Erom Silesia, in 

 carbonaceous shales of the Lower Coal-measures. 4. Erom two places in Lancashire, in 

 cannel-coal of the Middle Coal-measures, and in bituminous shale of the Lower Coal- 

 measures. 5. Erom near Chesterfield, Derbyshire, in carbonaceous shale of the Lower 

 Coal-measures. 



Differences of outline are to be observed among the various individuals ; and some of 

 these variations appear to be limited to one or other of the groups of specimens from the 

 five localities mentioned. It is convenient, therefore, to seize these distinctions, slight as 

 they are, and certainly not of specific value (nothing of the body and limbs of animals 

 remaining to help our judgment), and make them serviceable in the recognition of the 

 several very similar forms of carapace from widely separate places, and from at least four 

 distinct horizons in the Carboniferous group of strata. 



^ As the smaller specimens are not found iu company with the larger E. striatce, I have kept them 

 specifically apart. "Were it otherwise, no distinction of great value could be easily described, and they might 

 be regarded as young forms. 



