CONTRIBUTIONS TO INVERTEBRATE PALEONTOLOGY NO. 5: 
TRIASSIC FOSSILS OF SOUTHEASTERN IDAHO. 
By C. A. WHITE, M. D. 
The fossils discussed and illustrated in this paper are those which 
were under the designation of TIossils of the Jura-Trias, described in 
the Bulletin of this survey, vol. v, pp. 105-117; having all been col- 
lected by Dr. A. C. Peale, assisted in part by Mr. J. EH. Mashbach, in 
1877. ‘The fossils in question were obtained in Southeastern Idaho; 
and a part of the species, especially the Cephalopods, have been found 
at no other than the localities which furnished the type specimens. A 
part of the Conchifers, however, had been previously found by Dr. 
Peale at other localities, not many miles distant, in Southeastern Idaho 
and the adjacent portion of Wyoming; and one of the species, Aviculo- 
pecten idahoensis, had been described by Mr. Meek. The strata of the 
localities last referred to had been by common consent assigned to the 
Jurassic period by the geologists who had visited them; or, ‘latterly, to 
the Jura-Trias, in consequence of the growing opinion that no paleonto- 
logical plane of demarkation exists between those series of strata which 
have hitherto been assigned respectively to the Jurassic and Triassic 
periods. I had adopted this latter view for the reason indicated, and 
in the first publication of these fossils I referred them to the Jura-Trias. 
The distinct Triassic character of this small fauna, however, as well as 
that of the one previously discovered in Nevada and California by King 
and Whitney respectively, seems to warrant the entire separation of the 
strata containing those foun from the Jurassic, and their reference to 
the Triassic. This view finds support also in Dr. Peale’s observations 
concerning the position of the strata from which he obtained these 
fossils, in relation to those which contain the undisputed Jurassic fossils 
above, and the Carboniferous strata beneath. I have, therefore, in the 
title of this article, referred the fossils of which it treats to the Triassic 
period. 
Among the species which are generally regarded as characteristic of the 
true Jurassic strata of the West are Pentremites asteriscus, Belemnites den- 
sus and Camptonects bullistriatus of Meek & Hayden, and Humicrotis curta 
Hall; and these species were obtained from some localities in the region 
within which the fossils of this article were obtained; but not from the 
same strata, with the apparent exception of EL. curta. Indeed the fauna 
of the strata which bear the fossils discussed in this article is quite dis- 
tinct from any other known in that great region, and, according to the 
observations of Dr. Peale, they occupy a distinct horizon much lower 
than that of the characteristic Jurassic fossils before mentioned. He 
places this horizon beneath the Red Beds, or the formerly accepted 
Triassic, and above the Carboniferous. The foiiowing remarks are based 
minainly upon his observations. 
Anong the exposures of Triassic strata in Southwestern Idaho and 
105 
