14 FOSSIL ESTHERI^. 



1. ESTHERIA MEMBEANACEA, I'acU, Sp. PL I, figS. 1 — 7. 



PosiDONOMYA, d'Eichwald. Geology of Russia, (published in the Russian language), 1846, 



p. 399. 

 AsMUSiA MEMBRANACEA, Pucht. Der Devonische Kalk in Li viand, 1849, p. 44. 

 PosiDONOMYA MEMBRANACEA, PacA^. Ucber Dimerocrinites oligoptilus, 1852, p. 26; and 



Der Devon. Kalk. Livland, 2nd edit., 1859, 

 p. 44, fig. 7. 

 — KUGOSA, Kutorga. Geognostische Karte des Gouvernements von Petersburg, 



1852. 

 EsTHEBiA, Bupert Jones. Quart. Journ. Geol. Soc, 1855, vol. xii, p. 376. 

 ? PosiPONiA RUGOSA {Kutorga). Von Helmersen. Geognostisch. Untersuch. mittl. Gouv. 



Russlands, 1858, p. 73. 

 EsTHERiA MuRCHisoNiANA, Bupert Joues. Quart. Journ. Geol. Soc, 1859, vol. xv, p. 



404, woodcuts, fig. 14, c, d (p. 408). 

 AsMUSiA MEMBRANACEA (Pacht.), Pander. Monographic ueber die Saurodipterinen, &c., 



1860, p. IV. 



Height of valve, about 1 inch ") ^ . , , 



, ^ , ' " [ Proportion 9 to 11, or 1 : 1 + 



Length, nearly .,.,\ „ J 



This species occurs both in Scotland (Caithness) and in Russia (Livonia and else- 

 where). 



I shall describe the Scottish specimens first : — 



Falves subquadrate, occasionally somewhat oblong in form, the majority being about 

 l-6th inch long and l-8th inch high, whilst some are as high as long. Pressure, however, 

 has interfered with the contours and proportions of many of these valves. The hinge-line 

 is straight ; the generality of the valves have the anterior and posterior edges forming 

 sharp angles with the dorsal line and passing vertically with a slightly convex outline to 

 the boldly rounded ventral border. In this case the umbo is distinct; almost, bat not 

 quite, in the middle of the dorsal line ; and bordered by a triangular depressed, but not 

 produced, ear on either side; the valve resembling somewhat that of a miniature 

 Posidonomya, or upper valve of an Avicuh-pecten. 



The surface is wrinkled, by about 18 to 20 concentric, rounded, closely set wrinkles, 

 uniform with the outline of the ventral border and extremities of the valve. The wrinkles 

 are coarsest near the umbo, their starting point, and they become finer as they approach 

 the edges of the valve. 



Under the microscope, between the broad wrinkles are seen, here and there, thin sharp 

 ridges lying in the narrow furrows ; and the patches of the outer surface, here and there 

 retained, are seen to be of a dark-brown opaque substance, exhibiting on and between the 



