FOSSILS OF THE CARBONIFEROUS. 215 
The Carboniferous form is associated with Productus Cora, P. semire- 
ticulatus, P. muricatus, P. elegans, Spirifera Rockymontana, S. camerata, ete. 
Formation and locality—Lower portion of Lower Carboniferous lime- 
stone, in canon directly south of a small conical hill on east side of Secret- 
canon-road Canon, Eureka District, Nevada. 
Genus SPIRIFERA Sowerby. 
Spirifera trigonalis Martin (Sp.). 
Plate xviii, fig. 11. 
Conchyliolites anomites trigonalis Martin, 1809. Pet. Derb., tab. xxxvi, fig. 1. 
Spirifer trigonalis Sowerby, 1820. Min. Con., tab. 265, fig. 1 (not 2 and 3). 
Spirifera trigonalis, var. 2, McCoy, 1855. Brit. Pal. Foss., p. 423. 
trigonalis Davidson, 1858. Brit. Carb. Brachiopoda, p. 29, pl. v, figs. 25- 
34; 35-372 
bisuleata Davidson, 1861. Ibid. Mr. Davidson gives the synonomy up to the 
date of his publication, 1858, also that of Spirifera crassa De Koninek, Spiri- 
Sera grandicostata, and S. transiens McCoy, which he regards as forms of this 
widely varying species. 
Spirifer increbescens Hall, 1858. Geol. Surv. Towa, vol. i, pt. 2, p. 706, pl. xxvii, figs. 6a-i. 
After a most careful study of a large series of specimens of this species, 
Mr. Davidson has united all the forms previously placed under the species 
mentioned in the list of synonyms as variations of a single very variable 
species and, in speaking of the winged, simple form and the transversely 
oval, rounded, thickened variety crassa, says: “The notion of both being 
the modification of a single species will, to the generality of observers, 
appear absurd ; still if we find every variation connecting these extremes, 
are we to refuse the evidence of our eyes and senses, and to create as many 
species as we possess specimens?” An examination of Mr. Davidson’s beauti- 
ful illustrations cannot fail to convince one of the specific relationship of 
the different forms, and I have no doubt that the Nevada shell before me is 
one of the varieties of this widely-distributed species. 
In the Mississippi Valley it is found in the Chester limestone of the 
Lower Carboniferous formation of the State of Illinois, and described by 
Professor Hall as Spirifera increbescens. Mr. Davidson states that it is 
abundant in England, Ireland, and Scotland, and that on the Continent it js 
found in Belgium. 
