BRACHIOPODA. 69 



advena* These are all from the Etage D, and should they prove referable to 

 Obolella, will constitute the latest recorded appearance of the genus. 



The American species which can safely be classed as Obolella are the fol- 

 lowing : 0. chromatica, Billings, 0. crassa, Hall, 0. Circe Billings, O. gemma, 

 Billings, and probably 0. polita,-\ Hall.i Of other species referred to the genus 

 by American writers, it may be remarked : 



0. ? ambigua, Walcott,§ will probably prove referable to the genus Elkania, 

 as suggested by the author of the genus, Mr. Ford.|| 



0. calata. Hall, = Lin gulella calata {Orbicula celata, HallTT). 



O. cingulata, Billings, ^ Kutorgina cingulata. ■ 



0. desiderata, Billings,** is the type-species of Elkania. 



0. ? discoidea. Hall and Whitfield ;f f generic character in doubt, as the interiors 

 are not known. 



0. ? Ida, Billings,:|:J is imperfectly known. 



0. ? misera, Billings,§§ is referred to the genus Linnarssonia, by G. P. 

 Matthew.IIII 



0. nana, Meek and Hayden.TIlT Mr. Walcott is disposed to consider this 



* Syst; Sil. Boheme, pi. 95, fig. iv. 



t The Zingula prima (Conrad's MS. description, first published "by Hall, Pal. N. Y., viil. i, p. 3. 1847), 

 from the Potsdam quartzite at Ausable Chasm, N. Y., has been i-eferred by Mr. Whitfield (Bull. American 

 Museum Nat. Hist,, vol. i. No. o, p. 142. 1SS4) to the genus Obolklla, and is also identified by him with 

 the species 0. ? polita, Hall, from the yellow pulverulent sandstones at Ti'empaleau, Wisconsin, so that, 

 should this identification hold good, the latter name will become a synonym of the foi-mer. The identifica- 

 tion is, howevei', made solely on the basis of external similarities, and must Vje regarded as subject to such 

 modifications as the interior charactei's, when known, may require. These have not been satisfactorily 

 demonstrated in the New York species, but there are specimens before us which inrlicate that its muscular 

 impressions are moi'e neai-ly those of Lingulella than of Obolella. The Obolella nitida of Mr. S. W. Ford, 

 also considered by Mr. Whitfield a synonym of the same species {op. eit.), appeal's, from an examination 

 of the type-specimens, to be a totally distinct fossil. 



I Under the name Obolella Atlantica, Mr. Walcott has mentioned, without giving a detailed description, 

 an additional species from the Olenellus zone. Conception Bay, Newfoundland (Proceedings U. S. National 

 Mus., vol. xii, p. 36. 1889). 



§ Palaeontology Eureka District, p. 67, pi. i, figs. 2 a-c. 1884. 



II American Journal, vol. xxxi, p. 467. 1886. 



1[ Palaeontology N. Y., vol. i, p. 290, pi. Ixxix, fig. 9. 

 ** Palffiozoic Fossils, vol. i, p. 69. 1862. 



tt Geographical and Geological Exploration Fortieth Parallel, ji. 205, pi. i, figs. 1, 2. 1877. 

 II Palaeozoic Fossils, vol. i, p. 71, figs. 63 a, b. 1862. 

 §§ Palseozoic Fossils, vol. ii, p. 69. 1874. 



III Illustrations Fauna St. John Group, No. iii, p. 35. 1885. 

 ^1[ Palaeontology Upper Missouri, p. 4, pi. i, figs. 3 a-d. 



