1:20 GEOLOGY. 
Locality and formation. This fossil occurs in immense numbers in a coarse brown calcareous 
randstone in the Lower Cretaceous strata at Oraybe, one of the Moqui villages. The number 
of the shells is so great as to make up a large part of a stratum three feet in thickness, their 
very abundance rendering it difficult to obtain good specimens. The general appearance is so 
striking that I have thought it best to call attention to it, that it may be hereafter recognized, 
and serve as a means for the identification of strata. 
It is associated with Ammonites percarinatus and a small Gryphea, probably identical with 
G. Pitcheri, but too imperfect for determination. G. Pitcheri, var. navia, occurs in the same 
strata within two or three miles of Oraybe. 
GRYPHAA. Lamarck. 
Gryeuma Prrcnert, Morton, Synopsis, p. 55, Pl. XV, jig. 9. 
This characteristic fossil occurs in bands of brown concretionary limestone interstratified 
with green shales, yellow sandstones and lignite beds, a few miles east of Fort Defiance. Still 
further eastward, near Covero, it is found in the same strata, and in Cretaceous limestones on 
the banks of the Pecos, east of Albuquerque. In Texas it occurs in great abundance in many 
localities. The Cretaceous strata of Nebraska do not contain it. It is generally found in the 
lower part of the Cretaceous series in Western New Mexico, in the equivalents of Nos. I and II 
of Messrs. Meek and Hayden’s Cretaceous section. This is the typical form of the species as 
given by Morton. 
Grypuma Pircuent, var. NAvVIA. Hall, P. BR. RB. Repts., vol. IIT; Geol. Rept., p- 500, Pl. I, 
jigs. T-10. 
I found the narrower form of G. Pitcheri at the Moqui villages associated with Ammonites 
percarinatus; subsequently, in the same formation east of Fort Defiance, and I have specimens 
collected on the Pecos. 
This shell should perhaps be considered specifically distinct from the preceding, as the dif- 
ferences which it exhibits from the typical form of G. Pitcheri are as striking and constant as 
those that serve to distinguish several species of Gryphea. It is true, however, that the 
specific determination of all the oysters is peculiarly difficult and unsatisfactory, from their 
great variation in size and form, and the absence of sharp lines, numerical parts, and geometric 
proportions, which so much facilitate the diagnoses of species in many families of mollusks. 
As a consequence, these shells should be carefully scrutinized when used as paleontolog | 
evidence, and deductions made from them should be given their proper subordinate value. 
ALLORISMA. King. 
ALLORISMA CAPAX, (n. sp.) 
Plate I, figs. 9 and 9a. 
Shell large, sub-elliptical, somewhat arcuate, thick, marked exteriorly with parallel lines of 
growth by which it is somewhat undulated; very inequilateral; anterior end thick, abruptly 
rounded from the beaks; posterior end flattened and slightly narrowed; beaks nearly terminal, 
prominent; hinge-line following the curve of the opposite margin, lowest in the centre; impres- 
sion of anterior adductor muscles large, rounded, placed near the anterior margin, projecting 
by early the entire diameter above a line drawn horizontally through the shell; greatest trans- 
erse diameter posterior to the beaks and above the middle; pallial impressions not visible. 
ength of cast, 4.42 inches; transverse diameter, 1.54 inch; vertical diameter, 2.25 inches. 
The only specimen I have of this fossil is a cast which retains but a small portion of the 
