BRACHIOPODA. 69 



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

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



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

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

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

 by American writers, it may be remarked : 



O.? ambigua, Walcott,§ will probably prove referable to the genus Elkanma, 

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



0. calata, 'Ro\\,^^= Lingulella calata {Orbicula c.alata, HallH). 



0. cingulata, Billings, = Kutorgina cingulata. 



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



O. ? discoidea, Hall and Whitfield ;ff generic character in doubt, as the interiors 

 are not known. 



0. ? Ida, Billings,ii is imperfectly known. 



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

 Matthew.IIII 



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



* Sjst. Sil. Boheme, pi. 95, fig. iv. 



t The L'mgula prima (Conrad's MS. description, first published by Hai.l, Pal. N. Y., vol. i, p. 3. 1847), 

 ffom the Potsdam quartzite at Ausable Chasm, N. Y., has been referred by Mr. Whitfield (Bull. American 

 Museum Nat. Hist., vol. i. No. .5, p. 142. 1884) to the s;enus Obolklla, .and is also identified by him with 

 the species 0. ? polita, Hall, from the yellow pulverulent sandstones at TrempHleau, Wisciinsin, so that, 

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

 tion is, however, made solely on the basis of external similarities, and must I)e I'egarded as subject to such 

 modifications as the interior characters, whtm known, may require. These have not been satisfactorily 

 demonstrated in the New York specie.s but there are specimens before us which imlicate that its muscular 

 impressions are more nearly those of Lingdlella than of Obolblla. The Obolella nitida of Mr. S. W. Fokd, 

 also considered by Mr. Whitfield a synonym of the same species (op. cit.), appears, from an examination 

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



t Under the name Obolella Atlantica, Mr. Walcoti' has mentioned, without giving a detailed descniition, 

 an additional species fiom the Olenellus zone. Conception Bay, Newfoundlaml (Proceedings U. S. National 

 Mus., vol. xii, p. 3(3. 1889). 



§ Palseontology Eureka District, p. G7, pi. i, figs. 2a-c. 1884. 

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

 ^Paleontology N. Y., vol. i, p. 290, pi. Ixxix, fig. 9. 

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



tt Geographical and Geological Exploration Fortieth Paralh-1, ;. tinr.. i.l i. ti .rs. 1. 2. I'^ll. 

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

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

 11 lUusti'ations Fauna St. John Group, No. iii, p. 3'). 1885. 

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



