886 THE PALEONTOLOGY OF MINNESOTA. 



IBucanla lialli. 



Among the species of the B. lindsleyi section it is common to find that the 

 obliquely revolving lines are sharply interrupted by the regular development of 

 lamellae 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 in the 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. inte.rta 

 are typical of the genus; B. 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 />'. r.rpunsa belongs 

 to Salpingostoma . 



BUCANIA HALLI, n. sp, 



PLATE LXVI, FIGS. 4-8. 



Shell 20 to 30 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 lamellae, 

 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. 



