108 GEOLOGICAL SURVEY OF THE TERRITORIES. 
augusta Hall & Whitfield, Aviculopecten idahoensis Meek, and Hunicrotis 
curta Hall. I am not entirely satisfied of the identity of the species here 
referred to 7. augusta, and there is a possibility that the Humicrotis is 
not HL. curta ; but so far as can be at present determined, it is identical. 
According to European standards the Cephalopods here described are 
unquestionably of Triassic types, and, as pointed out by Professor Hyatt 
in the following remarks, they have more resemblance to certain Ceph- 
alopods of the Muschelkalk or Middle Trias of Europe than to any other. 
The Triassic fauna discovered by King and Whitney respectively in Ne- 
vada and California was referred, and doubtless, correctly so, to the 
Upper Trias, and it was expected, in case a Triassic fauna should be 
found in the Rocky Mountain region, that it would also be referable to 
the Upper Trias. There was, however, apparently no special reason for 
such an opinion except that the evidence of the existence of any true 
Triassic fauna had so long escaped detection in North America, although 
the full series of strata had apparently been thoroughly examined at 
‘hundreds of localities, and over a very wide area; and the Upper Trias 
fauna referred to was the only one then certainly known to exist in North 
America. 
The Cephalopods of this collection were placed in the hands of Prof. 
Alpheus Hyatt for examination, the results of which are included in the 
following pages. Three of these forms, together with certain other 
European species, Professor Hyatt regards as constituting a separate 
genus, to which he has applied the name Meekoceras. 
BRACHIOPODA. 
Genus THREBRATULA Llhwyd. 
TEREBRATULA SEMISIMPLEX White. 
Plate 31, figs. 3 a, b, and e. 
Terebratula semisimplex White, 1879, Bull. U. S. Geol. Sur. Terr., vol. v, p. 108. 
Shell small, obovate or subelliptical in marginal outline; width less 
than the length; cardinal slopes gently convex or faintly angular ; mar- 
gins of the shell obtuse; both valves somewhat regularly, and nearly 
equally convex; beak of ventral valve moderately prominent, with the 
usual curvature over that of the dorsal valve, and with the usual apical 
perforation. Sila 
Shell-structure minutely punctate. Surface of both valves marked 
by numerous small radiating plications, sometimes slightly irregular in 
. Size, with the intervening spaces about equal in width with the pli- 
cations. These plications never reach the beaks, and sometimes they 
are so faint, and extend so short a distance from the front margin 
that the shell appears almost plain. The surface is also marked by the 
usual lines of growth. 
; Length, 14 millimeters ; breadth, 11 millimeters ; thickness, 9 millime- 
ers. 
The form, and more especially the plications, of this shell give it the 
appearance of certain forms of Rhynchonella, but its punctate structure 
forbids its reference to that genus. Perhaps it is really a Waldheimia ; 
but as the internal structure is not known, it is at present referred to 
the typical genus of the Terebratulidee. 
