850 THE PALEONTOLOGY OF MINNESOTA. 
[Bucaniide. 
MrcaLompHata, n. gen. (Ulrich.) This name is proposed for the widely umbili- 
cated group of species which Koken has provisionally designated as the “Gruppe 
des Bellerophon contortus.” The general form of the shell and volutions in these 
species is precisely as in the typical section of Bucania, as here restricted and 
defined. They may, however, be distinguished at once by the total absence of 
revolving surface sculpture. The apertural slit also appears to be much shorter, 
though the slit-band is well developed. In the last respect they agree with our 
Tetranota, but the expression in general is different, while the absence of the 
four reyolving dorsal ridges, which are such a striking feature of that genus, 
must, for the present at least, be regarded as forbidding their reference to 
Tetranota. Again, they remind one of Owenella, but the presence of a distinct slit- 
band, which is wanting in that genus, is sufficient to distinguish them. These 
varied resemblances, however, probably give us a reliable clue to the developmental 
history of the Bucaniide. At present the line of evolution appears to be from 
Owenella to Megalomphala to Bucania to Salpingostoma to Tremanotus. Tetranota 
to Kokenia and Oxydiscus to Conradella are separate lines. 
Hichwald’s Bellerophon contortus may be regarded as the type of Megalomphala. 
Excepting the doubtful Chazy species which Hall in 1847 called Bucania rotundata, 
and which may belong in this connection, the genus is not known to occur in 
American strata. In Europe, according to Koken, it is represented by Bellerophon 
contortus Eichwald and B. vaginati Koken, in the Lower Silurian, by B. taenia Lind- 
strém, in the Upper Silurian, and by B. macromphalus A. Roemer, in the Devonian. 
That the last really belongs to Megalomphala requires confirmation. 
Bucania, Hall (restricted). Shell consisting of three to five more or less 
depressed volutions coiled in one plane, with generally a wide umbilicus and not 
greatly —never abruptly—expanded aperture. Surface markings consisting of 
equal or unequal revolving riblets and lines of growth, together producing a more 
or less cancellated appearance. Revolving lines wavy or wrinkled, oblique, 
especially in the umbilicus, crossing from the ventral side of a whorl! to the dorsal 
slit-band in the space of about one halfa volution. Frequently they are interrupted 
by strong lamelle, the wavy edges of which are parallel with the lines of growth 
and the apertural margin. Aperture transverse and somewhat reniform in the 
typical section, higher and relatively larger in the B. nashvillensis section. In the 
former the lips are thin, the outer one sinuate, and the sinus prolonged into a rather 
long narrow median slit; in the latter the inner lip is rather thick and the slit 
shorter. Slit-band distinct, raised or depressed. Type, B. sulcatina Emmons sp. 
