906 THE PALEONTOLOGY OF MINNESOTA. 
[Conradella obliqua: 
gist than he is usually credited with having been, that his name should be connected 
with the genus. Hence the name Conradella. 
CoNRADELLA OBLIQUA, %. Sp. 
PLATE LXVII, FIGS. 1—6. 
Shell discoid, small, commonly from 10 mm. to 15 mm., and not known to exceed 
20 mm., in diameter. Whorls three or four, enrolled so that the keel of each is 
partly imbedded in the base of the next; transverse section of whorls subcircular, or 
transversely elliptical, the dorsum (excepting the keel) sometimes slightly flattened. 
Keel sharply elevated, narrow, nearly 1 mm. high in the largest specimens, the 
summit with distant subimbricating lunule bordered on each side by a delicate 
raised line. Slit long, extending backward from the aperture almost half a whorl, 
having a length of fully 20 mm. in a specimen 14 mm. in diameter; borders of slit 
raised, though not as prominently as the keel farther back. Transverse, serrated 
surface imbrications crossing the whorls obliquely, seeming to sweep strongly 
backward from the umbilicus, without however forming a sinus on the back. 
Serrated edges moderately prominent, the elevation in no case exceeding 1.0 mm., 
being in most cases less than 0.5 mm.; behind each sinus a rib, dying out before it 
reaches the preceding lamina. ; 
On the inner volutions the transverse imbrications are crowded, but on the last 
the distance between them is increased so that the average at the keel equals about 
one-third of the width of the volution. Between the serrated edges the surface is 
very finely cancellated, the longitudinal lines being somewhat less distinct than 
the transverse. . , 
This species is readily distinguished from C. compressa Conrad, C. pannosa 
Billings and C. dyeri Hall by the obliquity of the transverse imbrications, and the 
greater width of the volutions. 
Formation and locality—Not uncommon in the Rhinidictya and Ctenodonta beds of the Black River 
group, at St. Paul, Minneapolis, Cannon Falls, Chatfield and Fountain, Minnesota. 
Collections.— Geological and Natural History Survey of Minnesota; E. O. Ulrich; W. H. Scofield. 
Museum Register, Nos. 4051, 6853, 7536. 
CoNRADELLA SIMILIS, ». sp. (Ulrich.) 
(Not figured.) 
This species is closely related to C. obliqua differing from it chiefly in the 
transverse section of the whorls. In that species the section is almost circular, but 
in the form which we propose to call C. similis it is broadly obcordate. This 
difference causes the keel to appear as less abruptly elevated, the slope on each side 
