98 ROYAL SOCIETY OF CANADA 
like these parts in the opercule of Hyolithes. The peculiar relief of 
this valve in the genera named is due to the flattening of the cardino- 
lateral slope. The raised part of the valve extending thence to the front 
is strongly suggestive of the “cone” in the opercule of Hyolithes. 
What we do not have in Acrothyra is the broad flattened posterior slope, 
the “ horizontal limb” of Barrande. (See figs. 14, 3%, 4 and 5.) 
MuscuLaR SYSTEM. 
In comparing the muscle scars of the Inarticulate Brachiopods 
with the supposed muscle attachment of Hyolithes, we at once find 
diversity. Barrande has supposed that the groove behind the cone, or 
the chevron, marks the place of attachment of muscles and that the pair 
of small scars ‘behind the umbo or summit of the “cone,” marks the 
place of a second pair of muscles.* 
Barrande could find no trace of scars on the inside of the tube to 
mark where the opposite ends of these muscles were attached, and so 
concludes that they may have originated in the fleshy body of the mol- 
lusc [worm]. With these remarks the author’s observations in a general 
way agree, but with some variations, viz. :— 
It is to be noticed that in the case of both sets of scars, the ridges 
on the inside of the opercule become higher and wider as the margin of 
the shell is approached, that is, it grew with the growth of the shell, 
and the need of a more powerful muscle; it would therefore seem more 
probable that the holdfast of the muscle was at the end of this ridge or 
“chevron,” and not along its side. From the end of the ridge the 
muscle would go directly downward into the tube, and here we suppose 
the attachment of the muscle to have been, (viz.: the end of the ridge). 
The considerations relative to the lateral muscles apply to the car- 
dinal muscles, whose ridge also becomes higher as it recedes from the 
apex of the “cone.” For this reason this pair of ridges sometimes have 
a dumbbell shape from the enlargement of the ends; sometimes they 
show a crescentic curve at the end, or they may take a V-form and carry 
their size and height more uniformly. We would therefore suggest the 
outer end of this ridge as the point of attachment of the cardinal muscle 
in Hyolithes. 
It would be quite in keeping with its relations to the tube worms 
that the opercular muscles of Hyolithes should be attached to the fleshy 
part of the body, but we are tempted to call attention to certain charac- 
teristics of the tube which may indicate that there was an attachment of 
the muscle to the side of the tube. In the angle where the dorsal and 
ventral sides meet we can see in a number of species longitudinal ridges 

1 Syst. Silur. Bohem, vol. III., p. 65. 

