no.1614.. NEW AND OLD CARBONIFEROUS FOSSILS—GIRTY. 299 
Weeks, collected most of our material from the phosphate beds of 
Idaho. 
Locality and horizon.—Phosphate beds, Montpelier, Idaho. 
Ty pe-specimens.—Cat. No. 53465, U.S.N.M. 
OMPHALOTROCHUS CONOIDEUS, new species. 
Shell rather small, seldom exceeding 25 mm. in diameter, consisting 
of 7 or 8 volutions. Spire high, 19 mm. in one large specimen, but 
about 15 mm. in most cases. Umbilicus large, open. General outline 
conical, with sides nearly fiat from apex to base. The peritreme sec- 
tion is approximately tetragonal, the upper and lower surfaces being 
more or less flat and subparallel, the inner surface nearly flat and 
perpendicular to them, and the outer also nearly flat, making an 
angle of about 60 degrees with the base. The junction of the external 
and lower surfaces forms a sharp, somewhat projecting carina, em- 
phasized above and below by shallow indistinct grooves. A low 
ridge is usually developed on the external side of the peritreme_ 
shehtly below the middle. Each of the mature volutions projects at 
its base a little beyond the upper edge of that which follows it. In 
but few instances is the upper edge of one volution flush with that 
which preceded, and in none has it been observed to extend beyond. 
The internal outline is circular, the shell being thickened to form the 
carina; and at the three other angles made by the surfaces of the 
peritreme. 
The growth lines indicate that the aperture had a sinus above and 
below the carina, with a projection along it. 
In most of the characters enumerated there 1s more or less varia- 
tion. The lateral surface of the peritreme is usually shghtly con- 
cave, but sometimes flat or convex. ‘The lower surface also is in some. 
cases more strongly rounded than in others, thus affecting the promi- 
nence and sharpness of the carina. ,The revolving ridge of the 
lateral surface is sometimes obscure, though usually distinguishable. 
In all other characters, as well as some of those enumerated, this 
species is closely alhed to O. ferrierd, so that the description of the 
former may be used for O. conoideus, with the following modifica- 
tions: Like O. ferrieri, the spire of the present form is truncated, and 
owing to the same cause. The height of the peritreme is considerably 
greater than in O. ferriert, because of the fact that the lateral surface 
is considerably oblique to the axis. It is, at the same time, slightly 
concave or flat, instead of being convex, although a slightly convex 
condition has sometimes been observed in shells referred to this spe- 
cles. The height of the shell is relatively considerably greater than in 
O. ferriert for these reasons. The upper volution, instead of the 
lower, projects at the suture. The lower surface is flatter than in O. 
