40 FOSSIL ESTHERI^. 



sharp. The number of the concentric furrows is very variable ; when there are only 6, 

 they are deep, large, and removed one from another ; when the number is double, they are 

 straight and placed near together ; it is then that the hinge-border becomes long and straight. 



" The shell is so thin and delicate, that it bears many irregular depressions over all its 

 surface. It is a little broader than long; the diameter is from 1 to 2 lines." 



Kutorga observes Qoc. cit.) that, in his specimens, there are 10 — 13 sharp, outstanding, 

 concentric wrinkles ; that the shell is very thin, and therefore seldom perfect, but occurring 

 mostly as impressions. 



M. D'Eichwald also figured and described in the same work (p. 942, pi. 37, fig. 13 a, 

 13 b), his Posidonomya JEos, previously termed by him Cydas JEos, in the ' Geogn. de 

 Russie,'^ 1S46, p. 466; and 'Bullet. Mosc' 1856, xxix, 2, p. 575; and Cytherifia JEos, 

 'Bullet Mosc.,' 1857, xxx, 2, p. 307. C. Eos is described as a very thin and friable little 

 fossil, occurring in brownish-grey shale near Burakova, in the Government of Kazan ; 

 half a line broad, and a fourth of a line long, equally rounded on both margins, and marked 

 with a little notch in front of the somewhat projecting umbo. In the ' Lethgea Ross.,' 

 Pos. Uos is said to measure 1^ line in one diameter, and nearly as much in the other, and 

 is thus described. 



" Testa minima, oblique ovata, vertice vix prominulo margini antico approximate, 

 cardinali margine subalato, postice obtuso, superficies tenuiter transversim striata." 



It seems to me quite possible that better materials might bear evidence of U. ewiyua, 

 E. Eos, and E. tenella, (page 31) being all of one and the same species. 



The nature of the habitat of E. exigua is obscure. Cytheropsis Pyrrha (see Appendix) 

 may have been marine (according to what is known of its congeners), or otherwise. 



5. EsTHEBiA PouTLOCKii, Joucs. Plate I, fig. 25. 



PosiDONiA MTNUTA, Portloclc. Report Geology Londonderry, &c., 1843, p. 469. 



Heiffht of valve, ^l-inch")^ . „» , .^ ^ ^^ 



" ^1 S Proportion 27 to 40, or 1 : \\ — 



Length nearly... -f^ „ ) 



It is with some doubt that I refer this unique fossil (a somewhat worn and imperfect 

 concave impression) to Estheria. Eor certain it does not belong to Estheria 7ninuta, which 

 will be presently described. Still, it may be the cast of an Estheria, with which genus its 

 outline and disposition of concentric wrinkles appear to be consonant. It is relatively 

 large, but E. striata and others are larger. Its wrinkles are broad, but not too broad 

 for an Estheria (see PL II, fig. 16). 



This species (which I have named after its discoverer, one of the most eminent of the 

 geological explorers of Ireland) appears to have been of a subovate form, narrowest behind ; 

 slightly curved on the ventral side, and straight on more than the central third of the 

 dorsal edge ; the umbo was a little in advance of the middle of the shell, the valve had 



^ Published in the Russian language. 



