NEW SPECIES OF CAMBRIAN FOSSILS FROM CAPE BRETON. 
577 
Schizambon priscus, n. sp. PI. V., figs. 4 a-d. 
Shell substance firm, corneous (or calcareo-corneous '?). Outline 
orbicular, and valves lenticular and of moderate depth. 
Ventral valve with a rounded umbo, the greatest depth in front 
of the umbo, about two-thirds from the front. About one-sixth or one- 
eighth from the posterior margin, the valve is perforated by an oval fora- 
men, in front of which two narrow diverging ridges run forward to the 
front of the valve, where they are about as far apart as one-quarter of 
the length of the valve. There is considerable variation in the'size and 
position of the foramen in the examples collected. Interior . — The 
foraminal passage is smaller within than at the outer surface of the 
shell, and is surrounded by a raised rim; from it two thread-like grooves 
run forward into the front of the umbonal cavity. (The ridges that 
run forward from the foramen on the outer surface of the shell are 
preserved as grooves on its inner surface.) The visceral callus, of a 
lenticular outline extends about half as far in front of the foramen as 
that is from the posterior margin ; it is crossed by two faint diverging 
ridges on each side, and is bordered by two lateral stronger ridges, 
widely diverging, that mark the position of the lateral muscles ; the 
length of these ridges is about one-third of that of the shell. Faint 
traces of vascular trunks are found in the lateral and posterior part of 
the shell and make a regular arch about one-sixth of the length of the 
shell, from its margin. The margin is flattened especially in the pos- 
terior half, toward the umbo. 
The dorsal valve is flatter than the ventral, and its umbo somewhat 
removed from the posterior margin. The central part of the valve has 
a flattened triangular space extending back towards the umbo ; as the 
lateral margins are flattened in the posterior half a low flattened ridge 
extends out on each side from the umbo to the mid-length of the valve. 
Interior . — This shows a broad flattened mesian ridge extending half 
way across the valve from the posterior margin, on each side of this 
about one-third from the back of the valve, and nearly that far apart, 
are obscure oval marks, probably indicating the position of the anterior 
adductor muscles. The margins of the valve are flattened behind. 
Sculpture . — This consists of sharply defined but very minute, con- 
centric and radiating ridges that form a delicate cancellated pattern ; 
on the highest part of the shell the concentric ridges are most distinct, 
