ESTHERIA EXIGUA. 39 



are unattainable^ I venture to disregard any apparent differences in figures and descriptions, 

 and to look upon our figured specimen as a young form of Estheria exigua, Eichwald, sp. 

 And I am confirmed in this view by receiving specimens of E. exigua and E. Eos associ- 

 ated on one piece of marb as above stated. 



The history of the species is as follows : — 



A small Estherian fossil, from Kargala, near Orenburg, Avas described (under Bronn's 

 name, Fosidonomya minuta) by S. Kutorga, in 1844 (Zweiter Beitrag zur Pateontologie 

 Russlands, in the 'Verhandl. d. R.-K. Mineral. Gesellsch. St. Petersburg,' Jahr 1844, 

 pp. 63, QQ>, 86, pi. i, figs. 1 — 5), as occurring in a hard, asli- and black-grey shale (the 

 laminas sometimes ^ inch thick, sometimes very thin, and the planes of bedding streaked 

 with copper-green), referred by Von Qualen to the lower group of the Zechstein-formation 

 of the Government of Orenburg. Kutorga carefully indicates at p. 86, what appears to 

 him to be points of difiFerence between the Russian and the German (Bronn's) specimens. 

 Remains of plants abound in this copper-shale ; they were termed Voltzia hrevifolia 

 (Brongn.) by Kutorga, but D'Eichwald has subsequently referred them to UUmannia 

 Bronnii, Goepp., U. Biarmica, Eichw., and Walchia hjcopodioides, Brongn. 



In 1855 ('Lethsea Rossica,' livr., 4, p. 231), D'Eichwald described his Bosidonomya 

 exigua}- as occurring in this cupriferous marl-shale of the neighbourhood of Kargala, in the 

 district o^ Bjelebei, government of Orenbm'g. This little fossil he found associated with 

 TJllmannia ; and he regarded it as being probably a freshwater Mollusc. In the ' Bullet. 

 Soc. Imp. Nat. de Moscou,' annee 1856, vol. xxix, seconde partie, p. 559, M. D'Eichwald 

 described P. exigua, as being very small, ovate, with the hinge-border lengthened back- 

 wards, the surface transversely wrinkled, with not more than eleven very fine punc- 

 tured wrinkles. In 1859 ('Leth. Ross.,' Hat. 6), after noticing the occurrence of a shell 

 referred by him to " Posidonomga minuta, Goldf.," in shale of apparently Carboniferous 

 age, near Izoume (Isjoum, 'Bullet. Moscou,' 1856, xxix, 2, p. 559), in the Government of 

 Kharkojff (p. 940), and after remarking that most palcEontologists still consider this little 

 fossil to be a Mollusc, M. D'Eichwald described his P. exigua (p. 941, pi. 40, figs. 4 a, 

 and 4 h), referring to Kutorga's previous account of it (see above), but suggesting that 

 Kutorga's figure (fig. 5) of " P. minuta enlarged " may perhaps be a young Unio umbo- 

 natus. The following is D'Eichwald's description of P. exigua ; 



" Teste exigua, ovata, cardinaH margine postrorsum prolongato, superficies sulcata 

 transversis sulcis concentricis, 6 vel 11 nee pluribus, tenuiter punctatis : — In the copper- 

 bearing sandstone of Kargala, Gov. Orenburg, associated with UUmannia Bronnii. 



" The little specimen figured (pi. 40, fig. 4 a, grand, nat. d, grossi) has the hinge- 

 border straight, and the umbo scarcely projecting at the middle of the border, Avhich, bent 

 in a little arc, and obtuse at the two sides, is ordinarily prolonged equally before and 

 behind; the fiurows form httle concentric strise to the number of 6 — 11, very fine and 



1 Previously described in the Russian language in the ' Geogn. Russie,' 18J6, p. 456. 



