BRACHIOPODA. 
23 
(e) 1877. 
(b) 1878. 
(e) 1878. 
(&) 1881. 
(e) 1882. 
{d) 1883. 
(e) 1883. 
(a) 1884. 
(h) 1884. 
(e) 1884. 
(&) 1887. 
(e) 1887. 
(b) 1888. 
(c) 1888. 
(&) 1889. 
if) 1889. 
(e) 1889. 
(&) 1890. 
(a) 1891. 
Sph-ifer {Trigonotreta). Meek. Geol. Expl. Fortieth Parallel, vol. iv, p. 88, jil. ix, fig. 6. 
Spirifera, Hartt. Dawson’s Acadian Geology, 3d ed., p. 300. 
Spirifer, Dawson. Acadian Geology, 3d ed., p. 292, fig. 91. 
Spirifera, Miller. Journal Cincinnati Soc. Nat. Hist., vol. iv, ji. 2. 
Spirifera, Whitfield. Bull. Amer. Mus, Nat. Hist., vol. i. No. 3, p. 47, pi. vi, figs. 13-15. 
Spirifera, White. Twelfth Ann. Rej). U. S. Geol. Survey, p. 165, p)l. xl, fig. 2. 
Spirifera, Hall. Twelfth Kept. State Geologist Indiana, p. 326, pi. xxix, figs. 13-15. 
Spirifera, Walcott’. Palaeontology of the Eureka District, p. 134. 
Spirifera, White. Thirteenth Kept. State Geologist Indiana, p. 132, pi. xxxv, figs. 3-5. 
Spiriftra, Walcott. Palaeontology of the Eureka District, p. 216, pi. xviii, figs. 4, 7. 
Spirifera. Herrick. Bull. Denison University, vol. ii, p. 45, pi. ii, fig. 22. 
Spirifera, Herrick. Bull. Denison University, vol. i, p. 44, pi. ii, fig. 23. 
Spirifei-, Herrick. Bull. Denison University, vol. iii, p. 44, pi. iii, fig. 26; pi. vi, figs. 6-7; 
vol. iv, pi. vii, fig. 2. 
Spirifer, Herrick. Bull. Denison University, vol. iv, p. 25, pi. ii, fig. 8. 
Spirifera, Nettelroth. Kentucky Possil Shells, p. 124. 
Spirifera, Nettelroth. Kentucky Fossil Shells, p. 113, pi. xi, figs. 6-11 ; pi. xii, figs. 5-11. 
Spirifei'a, Nettelroth. Kentucky Fossil Shells, p. 120, pi. ix, figs. 8-14. 
Spirifera, Worthen. Geol. Survey Illinois, vol. viii, p. 105, jil. xi, fig. 5. 
Spirifera, Whiteaves. Contributions to Canadian Palaeontology, vol. i, p. 221, pi. xxix, 
figs. 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 8. striatus, 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 lamellae are, as a rule, in¬ 
considerably developed, and there is no median septum in either valve. 
Spirifer (= Choristites) Mosqnensis, 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, 8. Grimesi, Hall, these are comparatively 
inconspicuous. 
The external ornamentation, the arrangement of the plications and the 
nature of their superficial sculpture, afford 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 ( 8 . prcemonens, sp. nov.) with low 
fold and sinus, similar to iS. Hungerfordi, Hall, of the upper Devonian. In the 
