BRACHIOPODA. 23 



(e) 1877. Spirifer (Trlgonotreta), Mekk. Geol. Expl. Fortieth Parallel, vol. iv, j>. 88, pi. ix, fig. 6. 



(fc) 1878. Spirifera, Haktt. Dawson's Acadian Geology, 3d ed., p. 300. 



(e) 1878. Spirifer, Dawson. Acadian Geology, 3d ed., p. 292, tig. 91. 



(6) 1881. Spirifera, Miller. Joui'nal Cincinnati Soc. Nat. Hist., vol. iv, p. 2. 



(e) 1882. Spirifera, Whitfield. Bull. Amer. Mus. Nat. Hist., vol. i, No. 3, p. 47, pi. vi, figs. 13-15. 



(d) 1883. Spirifera, yfaiTK. Twelfth Ann. Rep. U. S. Geol. Survey, p. 165, pi. xl, fig. 2. 



(e) 1883. Spirifera, Hall. Twelfth Rept. State Geologist Indiana, ]). 32G, pi. xxix, figs. 13-15. 



(a) 1884. Spirifera, Walcott. PaUBontology of the Eureka District, p. 134. 



(b) 1884. Spirifera, White. Thirteenth Rept. State Geologist Indiana, p. 132, pi. xxxv, Hgs. 3-5. 



(f) 1884. Spiriftra, Walcott. Pal:eontology of the Eureka District, p. 21(5, pi. xviii, figs. 4,7. 

 (h) 1887. Spirifera. Herrick. Bull. Denison University, vol. ii, p. 45, pi. ii, fig. 22. 



(e) 1887. Spirifera, Herrick. Bull. Denison University, vol. i, p. 44, pi. ii, fig. 23. 

 (6) 188!<. Spirifer, Herrick. Bull. Denison University, vol. iii, p. 44, pi. iii, fig. 26 ; pi. vi, tigs. 6-7 j 

 vol. iv, pi. vii, fig. 2. 



(c) 1888. Spirifer, Herrick. Bull. Denison University, vol. Iv, p. 25, pi. ii, fig. 8. 

 (b) 1889. Spirifera, Nettelroth. Kentucky Fossil Shells, p. 124. 



(/) 1889. Spirifera, Nettelroth. Kentucky Fossil Shells, p. 113, pi. xi, figs. 6-11 ; pi. xii, figs. 5-11. 

 (e) 1889. Spirifera, Nettelroth. Kentucky Fo.'sil Shells, p. 120, pi. ix, figs. S-14. 

 (b) 1890. Spirifera. Wdrthen. Geol. Survey Illinois, vol. viii, p. 105, pi. xl, tig. 5. 

 {a) 1891. Spirifera, Whiteaves. Contributions to Canadian PaU-eontology, vol. i, p. 221, pi. xxix, 

 tigs. 4, 5. 



Forms with plications on the fold and sinus. 



This may be regarded as the typical group of Spirifers as it includes the 

 type-species S. striaius, Martin. Furthermore it is the most richly represented 

 in species and at the same time is a most compact association, not presenting 

 any substantial variations. Its members are strongly impressed with the 

 typical spiriferoid characters which are maintained throughout its existence, the 

 group terminating abruptly at the close of palaeozoic time. In internal structure 

 variations are slight and unimportant. The dental lamellaB are, as a rule, in- 

 considerably developed, and there is no median septum in either valve. 

 Spirifer {= Choristiies) Mosquensis, Fischer, is an example of a very few medio- 

 plicate species which have the dental plates highly developed; but in its 

 closest ally in exterior characters, N. Grimesi, Hall, these are comparatively 

 inconspicuous. 



The external ornamentation, the arrangement of the plications and the 

 nature of their superficial sculpture, aflbrd a key to the subordinate grouping 

 of these numerous species and indicates several important subsidiary lines of 

 development. These species seem to have appeared as early as the Niagara 

 fauna, in which occurs a suborbicular form ( S. pramonens, sp. nov.) with low 

 fold and sinus, similar to S. Hungerfordi, Hall, of the upper Devonian. In the 



