IA. 



T.ir.noi* MdofMta 1 



Bucania by its wide -lit-!>and ;inl -traight revolving lines, while the first character, 

 together \\itli it- different (Hn<;inin-\\\n>) aperture excludes it from liuranopgis. 

 Having to describe a similar species from Minnesota, we have concluded to establi-li 

 a new genii-. /\'"'<;im, for their especial benefit. 



The vertical range of three of the species of Tefninnfn is more extended than 

 innal witli IIH(U<;;I. T.obsolda occur- in tlu> Vanuxemia bed of the Stones 



Kr.er group, in the t 'tenodonta bed of the Mlack Kiver gronp, and reappears; appar- 

 ently very slightly modified, in the Utica group at Cincinnati: '/'. 1>\<lormln occurs in 



the lowe.-t divi-i< f tin- St<mc- River group of Tennessee, in the Hlack River group 



in Minnesota ami Canada, and in the Trenton of Minnesota, Kentucky, Tennessee, 

 New York and i'.mala: /'. te.wrinata is found in the Vanuxemia bed in Minnesota, 



.-onsin am! Illinois, in the "Glade limestone" of Tennessee, and in the Fusispira 

 bed of the Trenton in Minnesota. T. -im-nsis is as yet known only from the 



Vanuxemia bed in Minnesota, Wisconsin and Illinois, while T. macra occurs in the 

 same bed at Minneapolis. 



p 



TKTRANOTA BIDORHATA Hull. 



IM.ATK I. XV. FI08. 10-tt. 



anemia IMonata HALL, 1847, Pal. N. Y., vol. I, p. 186. 



Shell usually about 12 mm. in hight, but the bight may exceed 20 mm., and 

 occasionally reaches 25 mm.; volutions two and a half to three and a half, vertically 

 compressed, -ublunate in section, the width for the inner volutions or in young 

 specimens a little greater than twice the bight; in old examples the increasing 

 altitude of the centro-dorsal ridges causes the width just behind the aperture to be 

 proportionally somewhat less; umbilicus large, deep, rather sharply defined, the 

 \M'!th generally about half of the greatest diameter of the shell; the latter dimension 



< the greatest width of the aperture about as three is to four. Aperture some- 

 what abruptly expanded laterally, the hight and width about as three is to seven; 

 -lightly indented by the preceding whorl; lips thin, the outer one with a moderately 

 deep emargination. taking up between one-fourth and one-third of the anterior 

 outline; depth of the same about one-fifth less than it- width. Dorsum with four 

 strong revolving ridges, the two central ones nearer each other than to the lateral 

 ones, and higher, the altitude also increa .idually to the aperture; between 



them lies the broad slit-band which is more distinctly concave on the shell than on 

 internal casts, the double ridge in the latter, particularly near the aperture, often 

 appearing as a broad and more or less flat-topped single ridge; on each side of the 

 central ridges there is first a broad groove, then an obtusely angular ridge, and 



