30 GEOLOGICAL SURVEY OF THE TERRITORIES. 
-eallus which covers the shell apparently little if any thickened upon the 
inner lip. 
Length, from the base of the anterior canal to the apex of the spire, 
19 millimeters ; breadth of body-volution, exclusive of the aperture and — 
euter lip, 9 millimeters; breadth, including the aperture and outer lip, 
but excluding the labial spines, 14 millimeters. 
The apices “of both the anterior and posterior canals, and also of the 
posterior labial spine are broken off in the type specimen, but the ante- 
rior spine is entire, and the others are evidently nearly so, the anterior 
spine being 19 millimeters in length. The portion remaining of the pos- 
terior canal projects 5 millimeters beyond the apex of the spire, and 
that of the anterior canal projects 7 millimeters beyond the anterior 
border of the aperture. The anterior and posterior canal-spines and 
the posterior labial spine are each about 13 millimeters in diameter, the 
anterior labial spine being about double that width at its mid- length 
where it is broadest. 
This shell appears to have borne no varices or tubercles upon the eal- 
lus-covering of the body-volution such as characterizes the type species 
ot Tessarolax. Mr. Gabb appears to have regarded that feature as of 
generic importance, but I am disposed to consider it as only a specific 
character. 
Perhaps no family of shells with which the paleontologist has to deal is 
more in need of careful revision than the Aporrhaide. Of the various 
genera and subgenera which have been proposed by different authors, 
some doubtless ought to be rejected, but that all should be discarded 
and the species all referred to Aporrhais, as is the custom of some an- 
thors, appears to be unadvisable. ‘The covering of the whole shell with 
callus, as in Lispodesthes and Tessarolaw seems necessarily to have been 
correlated with characters in the animal which would separate it gener- 
ally from such forms as those which American authors generally refer 
to Anchura. The character of the anterior and posterior canals and 
labial spines of such forms as Tessarolax distorta and T. hitzvi, seem also 
sufficient to separate them generically from Anchura, Lispodesthes, and 
other proposed genera of the Aporrhaide. 
Tessarolax and Lispodesthes are both entirely callus-covered forms, and 
both are yet known only in Cretaceous strata; to which also other forms 
of the Aporrhaidz seem to be restricted. Aside from zobdlogical con- 
siderations, perhaps the strongest conventional reason for retaining the 
generic¢ distinctions which have been recognized in at least a part of the 
Cretaceous forms of this family lies in the fact that they seem to be 
characteristic of the Cretaceous period. 
Position and locality—The species here described was obtained, ac- 
cording to the records of the United States National Museum, by Dr. 
hk. B. Hitz, from the Fort Pierre Cretaceous Group, at Fort Shaw, near 
Muscleshell River, Montana. The specific name is given in his honor. 
Genus LISPODESTHES White. 
LISPODESTHES? OBSCURATA (Sp. NOV.) 
Plate 11, figs. 7 a and b. 
Shell subfusiform; spire rather short, tapering with nearly straight 
sides to the apex; volutions six or seven, convex; last or body volution 
rather large, without a revolving angle; suture impressed ; outer lip or 
_ Wing comparatively small, as indicated by all the known specimens, its 
