PALMHOZOIC ROCKS IN CANADA AND SCOTLAND. 373 
giving simply those of which there are comparatively numerous 
examples. 
1. Comparatively elongated and narrow jaws, without any pro- 
minent anterior tooth, but with a series, sometimes more than 
twenty in number, of more or less similar teeth, which gradually 
diminish in size towards the tapering extremity of the jaw. This 
form of jaw in some instances is supported on a wide basal flange. 
2. Wide and flat, hollow jaws, with the two anterior teeth larger 
than those following, the posterior extremity truncate, and with a 
deep furrow or cavity extending nearly to the centre of the plate. 
3. Jaws mostly elongate, with a distinct, but not very large, 
anterior tooth or hook, which is immediately succeeded by a series 
of smaller teeth. 
4, Jaws in which the anterior hook is very largely developed, and 
the smaller teeth are on the generally straight edge of a wide plate. 
5. A simple, more or less curved hook, comparatively narrow 
throughout. 
6. A simple hook with a very wide flange-like extension poste- 
riorly. 
7. Sickle-shaped or crescentiform jaws, with a more or less deve~ 
loped rod-shaped extension at one end and a series of small teeth 
on the curved upper edge. 
8. Jaws flattened and subquadrate, also with a rod-like prolonga~ 
tion, the upper toothed edge nearly straight. 
9. Small, triangular, arched plates, with a series of teeth of very 
unequal dimensions. 
In attempting to classify these objects great difficulties arise on 
account of the detached condition of the specimens. As the muscular 
tissue by which they were attached to the gullet became destroyed, 
the various plates which compose the complicated jaw-apparatus of 
these animals were set free and scattered apart over the surface of 
the rock, and in not a single instance have I discovered the different 
plates in such a position as to indicate with certainty that they 
belonged to a single animal. This is the more remarkable from 
the fact that the isolated jaw-plates are in most beautiful preserva- 
tion, and could not therefore have been exposed to any very dis- 
turbing influences. When it isremembered that the compound jaw- 
apparatus of Annelids belonging to the existing family of the Hunicea 
is composed of five or six pairs of jaw-plates of different forms and 
sizes, it will at once be seen how complicated a task it would be to 
arrange a confused assemblage of these plates under the different 
individuals, species, and genera to which they belonged; but the 
work becomes still more perplexing in the case of fossil specimens, 
where there are at hand very probably only an incomplete scries of 
the different plates, and these may reasonably be supposed to vary 
from those of their existing descendants. Under these circumstances 
I have been obliged to describe the fossil jaws separately, but 
without assuming that each isolated piece belonged to a different 
species, or even, in some cases, to a different individual, though it may 
fairly be supposed, from the very numerous specimens, and their 
