198 STANTON—MOLLUSCAN FAUNULE. [April 3” 
and sometimes a few finer intermediate lines. A few individuals 
show five lines on the spire, while others have only three or two. 
Smooth forms like that represented by Fig. 10 usually show incipi- 
ent spiral lines on the last whorl. 
Height of an average specimen, about 17 mm.; greatest breadth, 
8 mm.; height of aperture, 7 mm.; breadth of aperture, 5 mm. 
The most striking feature of the species is the variability of its 
sculpture, though in this respect is comparable with such living 
species as G. virginica Gmelin. Of about 200 specimens in the 
collection nearly half either lack spiral sculpture or have it very 
faintly developed. 
The generic reference of Goniobasis is not entirely satisfactory, 
as the aperture differs in some respects from typical living species 
of the genus. It slightly suggests Lzop/acodes veternus Meek from 
the supposed Jurassic at the head of Wind River, but it is specifi- 
cally very distinct and I think not referable to the same genus. 
In sculpture it resembles G. ¢enuicarinata M. and H. from the 
Laramie more closely than any other fossil form. 
Locality.—Wettacombe’s ranch near Musselshell River, in the 
vicinity of Harlowton, Montana. 
_ Horizon.—Upper part of Lower Cretaceous or base of Up 
Cretaceous. 
GONIOBASIS? SILBERLINGI n. sp. Pl. IV, Fig. 6. 
A single fragmentary specimen associated with the preceding 
seems to be worthy of description, although the generic reference 
is very doubtful. It is the basal portion of a shell consisting of 
nearly two whorls and may be described as follows: 
Shell of moderate size, rather stout ; whorls very convex; aper- 
‘ture broadly ovate; inner lip thin, slightly reflexed below over a 
distinct umbilical pit ; surface of the spire with four strong spiral. 
ridges or carine, which are unequally spaced, the space between 
the uppermost one and the suture and also between it and its neigh- 
bor being broader than the other smooth bands. 
The fragment measures 13 mm. in height and 13 mm. in greatest 
breadth; height of aperture, partly estimated, 9 mm.; breadth of 
same, 6 mm. 
The base of the aperture is broken, and it is possible that the 
large size of the umbilical pit is due to abnormal individual devel- 
opment. If this isa normal example of the species, it can hardly 
