WHITE. _ TRIASSIC FOSSILS. 111 
number of examples of A. idahoensis Meek. The type specimens of this 
species, as before stated, were obtained at a locality in Lincoln Valley, 
about 50 miles northwestward from locality No.1. His description of 
it was published in the work already cited, and the strata from which the 
type specimens were obtained were then referred to the Jurassic. This 
form is sufficiently distinct as a species trom either of the other two 
that have just been described, but they are all three clearly congeneric. 
Although in outward characters and appearance they are like the typi- 
cal forms of Aviculopecten, the hinge is not known. All the specimens 
of all three of the species are preserved only in the form of casts of the 
left valve, and no trace of the right valve of either species, nor any 
hinge markings of any kind, have been detected. It is probable, as 
Meek has suggested in relation to A. idahoensis, that neither of the three 
species will, when their characters are completely known, be found to 
agree strictly with the typical forms of Aviculopecten. ‘Their reference 
to that genus is therefore to be regarded as provisional only. The fol- 
lowing is Mr. Meek’s original description : 
‘Shell suborbicular, very slightly oblique, hinge distinctly shorter 
than the valves. Left valve rather compressed ; posterior [anterior] ear 
very short or nearly obsolete, and scarcely angular at the extremity, the 
posterior [anterior] margin below being convex in outline instead of sin- 
uous; anterior [posterior] ear longer and more angular, compressed but 
more distinct from the slight swell of the umbo than the other, and hayv- 
ing its margin below broadly and rather slightly sinuous ; surface orna- 
mented by compressed, generally simple, alternately smaller and larger, 
radiating costz, only the latter of which reach the beak, while those of 
both series become nearly or quite obsolete on the ears, particularly on 
the posterior one; lines of growth small, rather regular and obscure. 
Right valve unknown. 
“This is probably neither a true Pseudomonotis nor an Aviculopecten ; 
but as I know nothing of the nature of its hinge, nor of its right valve, 
its true generic characters remain doubtful. Many paleontologists refer 
such forms to the genus Pecten, but they are evidently distinct from that 
group as typified by the existing P. maximus.” 
Among the fossils described in Contributions to Invertebrate Paleon- 
tology No. 7, upon a following page as Jurassic, and figured among 
Jurassic fossils on plate 37, is another species, A. superstrictus, evidently 
congeneric with the three foregoing species; and among them is also 
another shell, Vulsella (Modiolinu) macronota, which occurs associated in 
the same strata with it. It is quite probable that the strata from which 
these two species were obtained may prove to be equivalent with those 
strata from which the fossils came that form the basis of this article. If 
so, they are of ‘Triassic and not Jurassic age. This supposition is the 
more probable because both the types represented by the two species 
referred to occur in the Triassic, and are not yet known in the Jurassic 
of that region. 
CEPHALOPODA. 
Five species of Cephalopods, and perhaps six, are represented among 
the collections brought in trom localities No. 1 and No. 2, three of which 
belong to the genus here proposed by Professor Hyatt, and the others 
probably to Arcestes. The following are Professor Hyatt’s diagnostic 
remarks upon the proposed new genus; and following those are remarks 
upon each of the species, all of which are indicated by quotation marks, 
and followed by his initials in brackets. 
