GASTROPODA. 861 
Cyrtolites retrorsus.] 
its typical form the species is not known to occur in the Trenton, but a variety has 
been found in the Clitambonites bed of the Trenton group in Minnesota. For this 
we propose the subordinate name minor, the specimens being unusually small, none 
exceeding 11 mm. in diameter. The volutions seem also to be narrow, the hight at 
the aperture in the specimens at hand exceeding the width by about one-sixth. The 
surface markings are precisely as in the typical form of the species excepting that 
the transverse striz in crossing the dorsal carina are sometimes bent slightly 
backward. The variety is of consequence chiefly because it proves the existence of 
the ornatus type at quite as early a time as that in which the C. retrorsus lived. 
And this fact justifies us also in denying that C. ornatus was evolved from C. 
retrorsus. 
Formation and locality —The typical form is a common fossil of the Loraine and Richmond groups 
at numerous localities in Ohio, Indiana, Kentucky, Pennsylvania, New Yorkand Canada. At Cincinnati 
the shell is often covered by a parasitic bryozoan (Leptotrypa ornata Ulrich) which, when carfully chipped 
away, generally leavesa good cast of the surface markings and not infrequently the test itself. The 
species has not yet been certainly identified in the Utica group, but we suspect that one or two casts 
collected in the lower part of this group at Covington, Kentucky, may belong to it. Variety minor was 
found by E. O. Ulrich in the Clitambonites bed of the Trenton group, near Cannon Falls, Minnesota. 
CYRTOLITES RETRORSUS, 2. Sp. 
PLATE LXII, FIGS, 32—37. 
Shell rather small, the diameter rarely exceeding 15 mm., in one case 20 mm., 
in others mostly from 12 to 14 mm.; in general appearance decidedly like C. ornatus, 
the dorsal slopes being strongly undulated, and the surface distinctly reticulated. 
Carefully compared, however, it is found to differ in the following particulars: the 
keel is more prominent, the dorsal slopes are more concave, the sides sharper, the 
transverse section of the volutions more distinctly quadrangular, and their rate of 
increase greater. The most important difference is in the form of the mouth and 
the direction of the transverse surface lines, The mouth namely is deeply cut out 
and the lines instead of passing directly across the back are strongly curved back- 
ward. Finally there is a small ridge along the suture line that has not been 
observed in C. ornatus. The retral curve of the transverse lines is slightly greater 
than in C. carinatus Miller, with the typical form of which C. retrorsus agrees very 
closely so far as the inner volutions are concerned. But mature specimens of the 
two species cannot be confounded, the dorsal slopes in Miller’s species becoming 
flat with maturity, while undulations are not developed except in the oldest 
examples. In C. retrorsus, on the contrary, they begin very early, while the con- 
cavity of the dorsal slopes continues through all stages. 
There can be no reasonable question about the specific distinctness of this shell, 
nor do we doubt that it will include, if not all, at least a part of the Tennessee 
