NEAV SPECIES OF CAMBRIAN FOSSILS FROM CAPE BRETON. 
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inner edge of the flattened margin of the valve ; the “ j ” laterals are 
on the slope of the valve within the flattened margin. 
The vascular trunks extend forward in a regular arch from the 
middle of the valve a little within the flattened margin, which is 
creased transversely by about a score of closely set parallel grooves. 
In the anterior third these give place to grooves that are at right 
angles to the margin ; these correspond in course to the faintly im- 
pressed sub-parallel grooves that extend from the front margin across 
the middle of the valve to the visceral callus. Faint traces of branches 
of the vascular trunks are seen on the slopes of the valves in the 
anterior half. 
The dorsal valve is of an oval form. It is strongly arched down in 
the posterior half, but less so on the anterior slopes. Interior . — This 
shows at the cardinal lines a depression in which are a pair of circular 
pits, due to the cardinal muscles. Between these pits, on the axial 
line is a small pit from which two sharp low ridges run forward ; at 
one-third from the back of the valve there is a minute scar between 
these ridges ; and outside of them in the posterior half of the valve 
are the large oval prints of the central (“h ”) muscles; these are set 
somewhat diagonally to the axial line, having the fronts turned out- 
ward. At the anterior ends of the median ridges are the small scars 
of the anterior lateral (“j”) muscles. Faint diverging ridges extend 
from the umbonal cavity toward the lateral margins of the valves ; at 
one-third from the back, partly on and partly outside the ridges 
are the large but rather faint imprints of the posterior lateral muscles. 
This valve, like the ventral, has flattened margins on which are 
imprinted minute, closely set, transverse grooves. 
Sculpture . — The sculpture of the true outer surface of this species 
is not easily found ; it is imprinted on a thin calcareous, fibrous 
layer, which is usually broken away, revealing the next layer of the 
shell. The outer layer is traversed transversely by closely set striae, 
forming ridges of which there are about nine or ten in the space of a 
millimetre ; some of these ridges have cross striae at intervals, others 
anastomose, and all have a roughened surface ; the ridges have a 
waving course over the middle third of the shell, but elsewhere aie 
comparatively straight. 
Beneath the outer shell is a corneous layer whose sculpturing con- 
forms to that of the outer layer, but the striae are wider and the inter- 
