850 THE PALEONTOLOGY OF MINNESOTA. 



LBuoanlldae. 



MEGALOMPHALA, 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 revolving 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 Bucaniidce. 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. 



Eichwald'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- 

 strom, in the Upper Silurian, and by B. macromphalus A. Roemer, in the Devonian. 

 That the last really belongs to Megalomphala requires confirmation. 



BCCANIA, 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 half a volution. Frequently they are interrupted 

 by strong lamellae, 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. 



