MEDINAN, NIAGARAN, AND CHESTER FOSSILS 
79 
being distinctly less angular along the median part of the shell, 
resulting in a less triangular cross-section. Unfortunately the 
surface striae of the Edge wood species are unknown. 
Hormotoma trilineata Sp. nov. 
Plate XU, Fig. 6 
Spire attaining a length of 32 mm., and a width of 14 mm.; 
apical angle usually between 28° and 33°. The number of 
volutions usually is 10 or 11. The sutures form an angle of 
about 75° with the vertical axis of the shell. The slit-band is 
peripheral in position; its width varies from 0.6 to 1 mm. The 
upper margin of the slit-band tends to be at mid-height of the 
volution and to form its most prominent part, while the lower 
margin of this band lies along the lower slope of the volution, 
slightly closer to the axial part of the shell. The general form 
of the volutions varies considerably in different specimens. 
Usually there is a tendency toward angularity, the margins of 
the slit-band being elevated slightly above the general convexity 
of the volutions, sometimes with a faint concave curvature of 
the shell both immediately above and below the band. In some 
specimens the concave curvature immediately above the band 
is quite distinct and broad. In that case there may be a faint 
revolving angulation about 1.5 mm. above the slit-band. Above 
this angulation there may be a slight flattening of the general 
convexity of the volutions. At the sutures the surface curves 
abruptly inward. On the lower slope of the last volution, at a 
distance of 2.5 mm. from the slit-band, there may be a second 
faint angulation, usually stronger than the one described first. 
In by far the greater number of specimens the general convexity 
of the volutions tends to be angulated on approaching the slit- 
band, and the upper half of the volutions tends to be slightly 
conical in slope. 
Along the upper part of the shell the slit-band usually is 
trilineate, two very narrow sharp lines forming the lateral borders, 
and a broader line occupying the median line, or a position slightly 
above the median line of the band. The trilineate character 
