90 GEOLOGICAL SURVEY OF THE TERRITORIES. 
nearly flat beneath; umbo somewhat prominent, nucleus or apex pos- 
terior, minutely subspiral and depressed almost closely upon the poste- 
rior margin, small, closely incurved and turned towards the right side ; 
inner lip broad, smooth, slightly convex in all directions, and occupying ~ 
fully one-half of the whole under surface of the shell; outer lip appar- 
ently moderately thin, but this feature has not been clearly seen. Surface 
so nearly smooth as to give the shell an almost polished appearance, but 
under the lens minute striz of growth are visible; and also near the 
borders minute radiating stiiz are seen, apparently in the substance of 
the shell. There are, also, upon the only example yet discovered, seven 
or eight irregular radiating stripes of coloration of the test. These are 
now brownish in color, while the general surface is buff; both of which 
colors are doubtless now different from those which characterized the 
shell while the mollusk was living, but the pattern of ornamentation is 
no doubt correctly preserved. 
Length, 10 millimeters; breadth, 7 millimeters; height, 5 millimeters. 
This species resembles in many respects, WV. (V.) patelliformis Meek, 
especially the variety Weberensis White; but it differs from the former in 
_ Shape, and from the latter in being without any trace of radiating raised 
lines or costé, in the greater prominence of the umbonal portion, and its 
somewhat more conspicuous apex. Its coloration is not taken into ac- 
count in this comparison because its preservation in this species and 
not in the other is thought to be only accidental. 
Position and localityx—Laramie Group; Black Buttes Station, Union 
Pacific Railroad, where it was found associated with the majority of the 
species of Unio described in this article, besides Corbicula (Leptesthes) 
fracta, and other mollusks. 
Genus CERITHIDEA Swainson. 
Subgenus PIRENELLA Gray. 
CERITHIDEA (PIRENELLA) NEBRASCENSIS Meek & Hayden. 
For description and illustration of this species, see vol. ix, U.S. Geol. 
Sur. Terr. (4to ser.), p. 559, pl. 43. Dr. Hayden obtained the types, which 
are the only examples yet discovered, from Laramie strata, near the head 
of Little Missouri River. 
Genus GONIOBASIS Lea. 
Thirteen or fourteen specific fossil forms have been obtained from the 
strata of the Laramie Group in different portions of the great region 
which it largely occupies, which authors have generally referred to the - 
genus Goniobasis of Lea. ‘These species may be separated into certain 
more or less distinct groups by characteristics which they respectively 
possess. Two or three of these suggested groups possess characteristics 
which may, perhaps, prove to be of at least subgeneric importance, but 
more material is necessary before such a study of them can be satisfae- 
torily made. At present, three sections seem to be indicated, of which 
G. cleburni, G. nebrascensis, and G. gracilenta may be taken respectively 
as the types. Perhaps also the form which, in a following description, I 
have referred to Melania (M. wyomingensis) may be regarded as the type 
of only a section of Goniobasis co-ordinate with these, and not properly 
referable to Melania. At present, however, | prefer to make the follow- 
ing references of these forms, hoping at a future time to study them ex- 
haustively. 
