WHITE.] CRETACEOUS FOSSILS. 15 
the molluscan fauna of the Laramie period had mainly its genetic 
derivation from the estuary faunz that were established along the con- 
tinental shores of marine waters during the previous Cretaceous epochs. 
In view of what we already know of the history of the great Laramie 
deposit, this view of the genetic derivation of its molluscan fauna would 
seem to be the most natural one, even without the paleontological hints 
here mentioned. 
In the marine strata of the Cretaceous series at Coalville examples of 
an Anomia are not unfrequently met with which closely resemble this 
one, and which may really belong to the same species. All the examples 
from the marine strata there which have come under my observation 
are, however, too imperfect to show the surface markings, and thus an 
important specific characteristic is wanting. 
Position and locality.—The specimen figured on plate 12 is one which 
Mr. Meek obtained from the estuary strata of the Cretaceous series at 
Coalville, Utah. 
Genus PTERIA Scopoli. 
PTERIA?? STABILITATIS (sp. NOv.). 
Plate 17, fig. 3 a. 
Shell adherent by the whole surface of the right valve, suborbicular 
or transversely suboval in marginal outline; hinge-line straight, less in 
length than the breadth of the shell. Right valve thin, especially at, 
and near the margins; beak minute, hardly raised above the cardinal 
border; ears minute or obsolete; hinge-area narrow, ending somewhat 
acutely both anteriorly and poster iorly, its Inner border prominent but 
plain; cartilage-pit small, pyramidal, turned obliquely forward. Upper 
or right valve unknown. 
Breadth of the largest example discovered, 34 millimeters ; height of 
the same from base to cardinal border, 26 millimeters. Three or four of 
the examples are not above 14 millimeters in diameter. 
The only known representatives of this species are one adult and sev- 
eral small examples of the right valve adhering to the surface of a frag- 
ment of the shell of a large Inoceramus. It evidently belongs to the 
Aviculide, but in being adherent by the whole surface of the right valve 
it differs from all other known members of that family, and when perfect 
examples of both valves are discovered it will probably be found to rep- 
resent an unpublished genus. The shell-substance of the thin marginal 
portion of ajl these examples is loosely cellular, which condition is pos- 
sibly due to some malady which affected the mollusk while living, but it 
seems to be connected with a prismatic-cellular structure of the thicker 
portion, such as is common to the Aviculide. 
Position and locality.—Cretaceous strata, Collin County, Texas, where 
it was collected by Mr. 8. W. Black, and sent by him to the Smithsonian 
Institution. 
Subgenus OXYTOMA Meek. 
PTERIA (OXYTOMA) SALINENSIS White. 
Plate 16, figs. 2 a and DB. 
Pteria (Oxytoma) salinensis White, May, 1880, Proc. U. S. National Museum, vol. ii, p. 296. 
Shell rather large for a Cretaceous Pteria; the body, exclusive of the 
wings, being obliquely ae knead broad at base, moderately gibbous, dis- 
