BRACHIOPODA. 205 



Conrad.* The former has a very considerable range, appearing, according to 

 DAViDSONf in the Caradoc, Lower and Upper Llandovery, Woolhope, Wenlock 

 and Ludlow formations. 



\\\ America it has been found only in the Niagara group, while its congener, 

 Orlhis varica, Conrad, a very distinct species,:}: is confined to the Lower Helder- 

 berg fauna. 



DALMANELL A 



(uom. propos). 



X. Group of Orthis testudinaria, Dalman. 



PLATE VB, FIGS. 25-39; and PLATE Vc, FIGS. 1-47. 



1828. Orthi.'i, Dalman. Kongl. Vet. Acad. Handl., pp. 115, 117, pi. ii, tig. 4. 



1842. OHhia, Emmons. Geology of N. Y. ; Kept. Second Dist., p. 404, fig. 4. 



1842. Orthis, Vanuxbm. Geology of N. Y. ; Rept. Third Dist., p. 139, fig. 4. 



1843. Orthis, Atrypaf Hall. Geology of N. Y. ; Rept. Fourth Dist., p. 105, fig. 6; p. 175, fig. 4, and 



p. 271, fig. 4. 

 1843. Orthis, Conrad. Proc. Acad. Nat. Sci., Phila., vol. i, p. 133. 

 1847. Oi-this, Hall. Palceontology of N. Y., vol. i, pp. 117, 118, 120, 128, pi. xxxii, figs. 1, 2, 5, and pi. 



Ixxix, tig. 4. 

 1852. Oi-thU, Hall. PaU-eontology of N. Y., vol. ii, p. 152, pi. lii, fig. 3. 



1856. Orthis, Billings. Canadian Nat. and Geol., vol. i, p. 40, fig. 1, and p. 136, pi. 2, fig. 5. 



1857. Orthis, Billings. Rept. of Progress Geol. Surv. Canada for 1856, p. 296. 



1857. Orthis, Hall. Tenth Rept. N. Y. State Cab. Nat. Hist., p. 42, figs. 1, 2, and p. 44, fig. 1. 



1859. Orthis. Hall. PalfBontology of N. Y., vol. iii, pp. 168-172, jil. xii, figs. l-:il, and pi. xiii, fig.«. 1-12. 



1859. Orthis, Billings. Canadian Nat. and Geol., vol. iv, p. 434, fig. 10. 



1860. Orthis, F. Roemer. Sil. Fauna westl. Tennessee, p. 62, pi. v, fig. 7. 

 1860. Orthis, Hall. Thirteenth Rept. N. Y. State Cab. Nat. Hist., p. 121. 

 1862. Orthis, Hall. Geology of Wisconsin, vol. i, p. 42, fig. 7 and p. 436. 

 1862. Orthis, Billings. Palieozoic Fossils, vol. i, p. 79, fig. 72. 



1862. Orthis, Hall. Fifteenth Rept. N. Y. State Cab. Nat. Hist., pi. ii, figs. 1-3. 



1863. Orthis, Billings. Geology of Canada, pp. 130, 165, 231, 312, figs. 57, 144, 246, 320. 



1867, Orthis, Hall. Palaeontology of N. Y., vol. iv, p. 35, 46, 62, j.!. v, figs. 1, 2; pi. vi, fig. 1 and 



pi. viii, figs. 3-8. 



1868. Orthis, Meek and Worthbn. Geology of Illinois, vol. iii, p. 373, pi. vii, fig. 6. 



1873. OHhis, Meek. Paleontology of Ohio, vol. i, pp. 103, 109, 112, pi. viii, figs. 1-3, 5. 



1874. Orthis, James. Cincinnati Quart. Jour. Sci., vol. i, p. 19. 



1875. Orthis, Miller. Cincinnati Quart. Jour. Sci., vol. ii, pp. 20, 22, 24, 30. 



* The Orthis acutiloba of Ringubbekg is a form of 0. biloba in which the lubes are very divergent. All 

 stages of variation between this extreme and the normal form for the species are i-eadily detected in any 

 large collection. 



t British Silurian Bi-achiopoda, p. 208. 



X Davidson (Silurian Brachiopoda, p. 207) and Quenstedt (Petrefactenkunde Deutschlands, pi. Iv, figs. 

 67-70), erroneously regarded this species as indentical with 0. biloba. 



