858 THE PALEONTOLOGY OF MINNESOTA. 
[Cyrtolites, 
whorls but becoming less angular if not quite obsolete in nearing the apertural 
margin; slit-band occasionally distinguishable; outer lip of aperture thin, sinuate 
and notched centrally; inner lip entire where it touches the preceding volution; 
within the edge it is first deeply concave, then produced into a broad thick flattened 
plate or septum, which extends a considerable distance into the aperture; upper 
surface of septum with a low but well defined median ridge; inner aperture covered 
(always?) by a triangular flat operculum. Type, C. carinata Hall. 
C. acuta U. & §. Black River group. C. carinata Hall. Trenton group. 
C. minima U. & 8. Black River group. C. cunule Hall. Trenton group. 
QO. phalera Sardeson. Black River group. C. explanata Ulrich. Top of Trenton group. 
C. cymbula Hall. “Hudson River group.” 
Genus CYRTOLITES, Conrad. 
OCyrtolites, CONRAD, 1838, Ann. Rept. Nat. Hist. SULVAENG Yep dss 
Cyrtolites (part.), Hall, 1847, Pal. N. Y., vol. i, p. 187. Minuer, 1874, Cin. Quart. Jour. Sci., vol. i, p. 
308; also 1889, N. A. Geol. and Pal., p. 401. WAAGEN, 1880, Pal. Indica, 
ar pt. 2, p. 132. Lixpsrrom, 1884, Silurian Gastropoda of Gotland, 
For generic characters see page 846. 
Restricting this genus to species of the type of C. ornatus Conrad, we have 
an isolated group of a shells that we find most difficult to classify satisfactorily. 
Despite the fact that authors have so generally agreed in uniting with the group 
that other peculiar type which we separate as Conradella, there is in reality but 
very little reason for considering them as related and much less as identical. In 
discussing that genus on a following page it is shown, we believe, to the satisfac- 
tion of every fair-minded student that Conradella, with its long dorsal slit and 
imbricated lamellz, is nearer Bucania, Salpingostoma and Tremanotus than to 
Cyrtolites. Indeed, we cannot see how an unprejudiced comparison of Conradella 
and Cyrtolites can fail to impress the observer with the conviction that the two 
groups of species are not only generically distinct, but not even closely related. 
Cyrtolites has been loosely employed by most authors for symmetrically in- 
volute, disciform shells, having the dorsum carinate or angular and the umbilicus 
broad so as to expose the inner volutions. These characters pertain to several 
widely distinct genera, and to use them as characteristic of a single genus is to bring 
together a most heterogeneous assemblage of forms. Thus we have among the 
species that have been referred to Cyrtolites several belonging to Ozydiscus, Koken 
( Tropidiscus, Meek), a genus that is nearer Bucania and Bellerophon; several of 
Conradella, which, as we have said, is nearer Bucania; and all of the species com- 
prised in the new genus Cyrtolitina. Lindstrém and others have thought that 
Porcellia, even, is the same as Cyrtolites. With equal propriety we might refer to 
the same generic group also the recent genus! Atlanta! 
