882 THE PALEONTOLOGY OF MINNESOTA. 



LKokenla. 



Formation and locality. Stones River group, Beloit and Janesville, Wisconsin; Minneapolis and 

 St. Paul, Minnesota. 



Collections. Geological and Natural History Survey of Minnesota; University of Wisconsin; E. O. 

 Ulrich. 



Museum Register, Nos. 665, 5108, 7297, 7316, 7284. 



Genus KOKENIA, n. gen. 



Bucanella, KOKEN, 1889, N. Jahrbuch f. Mineralogie, etc., Beilagebancl vi, p. 389. (Not Meek.) 



For generic diagnosis see page 848. For remarks see the following specific 

 description and under Tetranota and Bucanopsis. 



KOKENIA COSTALIS, n. sp. 



PLATE LXIV, FIGS. 46-49. 



Shell small, about 10 mm. in hight; volutions enlarging (apparently) gradually 

 to the aperture, depressed, somewhat reniform in section, the hight and width 

 respectively as four is to six and a half; slit-band wide, flat, sharply defined, some- 

 what elevated; on each side the surface descends first into a broad concavity, 

 beyond which the slope continues, now with increasing convexity, to the sharply 

 rounded orsubangular edge of the umbilicus; the latter is deep, and about one-third 

 as wide as the greatest diameter of the shell. Surface with seven straight revolving 

 lines on each side between the edge of the umbilicus and the slit-band; the first 

 on each side of the latter weaker than the others. The slit-band show faint 

 evidence of having borne four or five very fine longitudinal lines. Transverse lines 

 very fine, about eight in 1 mm., running, with little curvature, obliquely backward 

 from the sides of the volutions to the slit-band, joining the same at an angle of 

 something like 45 degrees. 



We have seen but a single imperfect specimen of this species, and were it 

 not that it belongs to a very interesting and easily recognized type, we would 

 scarcely be justified in describing it. We regard it as closely related to Koken's 

 species esthona, which he, as we have already stated (pp. 849, 876), erroneously places 

 with Hall's Bucania bidorsata, in the genus Bucanella, Meek. Since Koken's species 

 is not a Bucanella and the bidorsata is the type of our Tetranota, the question arises, 

 can the esthona also be included in that genus? We will admit at once that they are 

 related forms, yet we think the answer must be in the negative, and for two reasons: 

 first, the aperture is much less expanded laterally in the species esthona and costalis 

 than it should be in Tetranota; second, the revolving surface lines continue to the 

 aperture and are too numerous to be considered as equivalent to the four constant 

 dorsal ridges of T. bidorsata. As there is no other genus in which the two species 

 might be placed, we propose a new one with the name Kokenia. 



