886 THE PALEONTOLOGY OF MINNESOTA. 
[Bucania halli. 
Among the species of the Bb. lindsleyi section it is common to find that the 
obliquely revolving lines are sharply interrupted by the regular development of 
lamellee whose wavy anterior edges are decidedly elevated and parallel with the 
margin of the aperture, of which indeed they represent previous stages. ‘The effect 
is considerably as inthe otherwise widely different genera Conradella and Cyrtolitina. 
The surface sculpture of Tetranota also, though of a finer pattern, is essentially of 
the same type. 
Of the species originally referred to Bucania by Hall,* B. sulcatina and B. intexta 
are typical of the genus; Bb. punctifrons Emmons sp., though provisionally retained 
in the genus, is a peculiar form having a reticulated surface sculpture very much like 
that of Cyrtolites ornatus; B. rotundata, if correctly described, belongs to Megalom- 
phala; B. bidorsata is the type of our new genus Tetranota; and B. expansa belongs 
to Salpingostoma. 
« 
BucaNIA HALLI, 7. sp. 
PLATE LXVI, FIGS. 4-8. 
Shell 20 to 830 mm. in hight, consisting of about three and a half depressed 
volutions; volutions increasing in size gradually to the aperture, gently convex on the 
back, subangular at the sides, slightly concave in the middle third of the ventral part, 
acutely subelliptical in section, and about twice as wide as high; umbilicus large, 
deep, well defined, with flattened slopes, and equalling nearly two-thirds of the 
greatest diameter of the shell. Aperture transverse, the hight usually not exceed- 
ing half of the width, acutely subelliptical, angular and narrow at the lateral 
extremities, and slightly indented below by the preceding volution; outer lip very 
broadly sinuate, medium slit not fully seen, probably a half volution in length. Sur- 
face with subequal revolving wrinkled ribs, averaging about seven in 5 mm.; the total 
number increasing with age by bifurcation and interpolation; in-the umbilicus, 
especially behind the anterior half of the last volution, the ribs are decidedly 
oblique, but on the back of the volutions they are nearly longitudinal; at intervals 
of 2 or 3 mm. they are interrupted by more or less distinct transverse lamella, 
running obliquely backward from the edge of the umbilicus to the slit-band which 
they join at an angle of about 65°. Slit-band narrow, in some specimens appearing 
as slightly elevated; in others the center is excavated. Casts of the interior are 
quite smooth. A small specimen is 20 mm. in hight; the aperture is 15.5 mm. wide 
and 7.5 mm. high; the greatest width of the inner volution (at edge of inner lip) 5.5 
mm. The surface markings are not perfectly retained by any of our specimens, 
* Pal. New York, vol. i, 1847. 
