94 ROYAL SOCIETY OF CANADA 
OBOLUS TORRENTIS (Plate 1, fig. 1).1 
This species, found in the shales enclosed in the volcanic rocks 
of the base of the Cambrian, is referred to the genus only on the 
basis of general form. The internal moulding of the shell is not 
known, but the depressed band on the median line of dorsal valve 
indicates a relationship to the following species: 
OBOLUS TRIPARILIS (Plate 1, fig. 2). 
This species from the base of the Lower Etcheminian, is easily 
distinct from the type of the genus by the advanced position of the 
anterior adductors of the dorsal valve, and the close association with 
them of the “7” laterals. In O. Apollonis the first named muscles 
are wide apart and the “7” laterals are far in advance of them. 
There is also in the Etcheminian form a small scar between these 
laterals from which, with them, the species takes its name. Of this 
scar the cause is not known, but in size and appearance it resembles 
those made by the “7” laterals. 
OBoLus piscus (Plate 1, fig. 3). 
This form by the arrangement of the central group of muscles 
anc the sculpture shows it relation to the preceding. Itis larger and 
more orbicular. 
OBOLUS ÆQUIPUTEIS (Plate 1, fig. 4). 
This Obolus also has the two pairs of scars of the central muscles 
of the dorsal valve, approximated, but the supposed “ 7” laterals are 
unusually large. It also has the small median scar that is found in 
the other two. The three form a series of closely related forms 
(Eoopouws). 
OBOLUS LENS-PRIMUS. 
This small Obolus is the initial form of a quite different series. 
The preceding three have the vascular trunks of the ventral valve 
wide apart as in Obolus Apollonis. In the series of which O. lens- 
primus is the oldest known form, the vascular trunks of this valve 
are approximated so as to resemble those of the Lingulepis. They 
may even be so close together as to enclose only a third of the area 
of the valve. 

1 The full description of this and the three following new species will 
be found in the author’s report to the Director of the Geological Survey 
of Canada, on the Cambrian Rocks of Cape Breton. 
