1030 THE PALEONTOLOGY OF MINNESOTA. 
LOphiletina sublaxa. 
broadly backward. Of the following two species, O. sublaxa may be regarded as the 
type. 
The principal, or perhaps we should say only feature relied on in distinguishing 
this new generic group from Ophileta on the one side and Huomphalus on the other, 
is the slit-band. Both of those genera may often have an apertural notch at the 
terminus of the ridge corresponding to the “band,” but there is never anything like 
a definite band, the lines of growth passing over the ridge without interruption 
further than is occasioned by changing their direction from obliquely backward to 
obliquely forward. In Ophiletina, however, as is shown in figures 41 and 47 on plate 
LXXIV, the ridge is as much of a “slit-band” as in the majority of the Lower 
Silurian Pleurotomariide. In Helicotoma, certain species of which are considerably 
like our Ophiletina angularis, the summit of the corresponding ridge, though never 
flat nor bearing lunule, is occasionally margined on each side by a delicate raised 
line, the result being a “band” that is not greatly different from the kind pertaining 
to species of Lophospira like L. acuminata (compare fig. 8, plate LX XIII, and fig. 24, 
plate LXXIV). Another constant and easily recognized difference between Ophiletina 
and Helicotoma is furnished by the course of the lines of growth across the vertical 
outer surface of the shell. In the former the lines curve forward in the upper half 
and just as much backward in the lower, the direction on the whole, therefore, being 
essentially vertical. In the latter the forward direction continues to the basal 
angle (compare plate LX XIV, fig. 46 with 15, 16, 22, 38 and 37). 
OPHILETINA SUBLAXA, ”. sp., and varieties. 
PLATE LXXTV. FIGS, 40—42 and 47. 
Shell small, 13 to 16 mm. in diameter, coiled approximately in one plane, the upper side flat, the 
lower gently concave; volutions slender, three in number, without the more or less prominent nucleus, 
hexagonal in transverse section, a little wider than high, the greater part of the last free. Of the six 
angles the strongest bears the band and lies at the outer edge of the upper side. Within this the space to 
the suture line is divided into halves, the outer concave, the inner a flat slope, by a second carina. The 
third is prominent and thin and lies considerably beneath the middle of the outer surface of which the 
fourth carina forms the base. The fifth and sixth angles are more obtuse, and lie one about the middle 
of the inner side, the other at the junction of the inner and lower sides. Lines of growth strong, equal, 
somewhat imbricating, averaging about seven in 2 mm., making a slight retral bend (it is often stronger 
than in our engraving) in crossing the central angle of the upper face, a very strong and sharp retral bend 
or loop on the sides and summit of the band-ridge, a slight forward curve on the outer and a retral curve 
on the lower surface. The band itself is convex and sharply defined, the lunuiz strong. 
The above description is strictly of the northwestern form of the species. Of this we have three 
specimens, one from each of the three states of Minnesota, Wisconsin and Illinois. We havea fourth 
specimen (original of fig. 42), found by one of the authors in the lower part of the Stones River group in 
Tennessee, which differs slightly in several particulars. In the first place the whorls are more slender 
when viewed from above; next the hight and width of the volutions are more equal; then the inner face 
of the whorls is steeper and rounded rather than angular; finally, the upper side of the shell is concave 
and the lower flat instead of the reverse. Possibly this Tennessee specimen, which, although a silicified 
