57 
course of direction of the striae. It differs from R . immaturum 
(Billings) in having fewer whorls, in the angle at the peripheral 
margin, in the shape and size of the umbilicus, and in the pro- 
nounced curves of the striae. 
Horizon and Locality . Chazy : Aylmer limestone at Mac* 
Laren landing. 
Leperditia trentonensis n. sp. 
Plate IV, figures 12, 13 
Figure 7. Leperditia trentonensis n. sp. 
A. View from above, showing outline. 
B. Profile of the specimen taken from the ventral margin, 
showing the spine-like tendency of the convexity of the 
shell. 
Length 8 mm. ; width 4| mm. 
The surface is smooth but not shiny. The eye-spot is 
very indistinct. The most striking feature is the abrupt in- 
turning of the convexity of the shell, just anterior to the centre 
of the ventral margin, almost producing a resemblance to a 
blunt spine when viewed in profile. 
In general outline this species differs from Leperditia 
canadensis louckiana in that it is on the whole less convex, and 
the maximum of its convexity is near the ventral margin. 
Except for the abrupt termination of its convexity, it is more 
closely in accord with Black River species of Paquette Rapids 
Leperditia canadensis paquettiana Jones, but it differs from it 
in being less convex and in being longer in proportion to its width. 
Paquette Rapids species, 7 : 4| mm. 
MacLaren Landing species, 8: 4§ mm. 
It differs from Leperditia ovata Jones in the position of its 
greatest convexity, in having the ventral and dorsal margins 
more nearly parallel, and in its proportionate length and width. 
Leperditia ovata , 7 : 5 mm. 
MacLaren Landing species, 8: 4§ mm. 
Horizon and Locality . Lowest Trenton at MacLaren landing. 
