On THE STRUCTURE AND CLASSIFICATION OF THE TREMATASPIDAE. 
13 
accounted for by the openings, either in tlie middle, or sides, of the dorsal shield. Moreover 
a renewed examination of Pteraspis lias convinced me that the projection at this point, 
shown so clearly by some specimens in the British Museum, is not due to the squeezing out 
of the matrix from an orbital opening, as A. S. Woodward maintains. It is due on the con- 
trary to a pronounced tubular projection of the shell itself, that is now partly worn, or 
broken off, leaving the matrix core exposed. How far this structure protruded in its unin- 
jured condition, or whether it was a jointed, movable appendage it is imposable to say from 
an examination of the lmown remains of this genus. However Lindstrôm’s most important 
discovery of a shield of Cyathaspis , side by side with part of an oar-like appendage having 
precisely the same sculpture, removes any doubt that may hâve existed as to the presence 
of paired movable appendages in Cyathaspis and related forms. These appendages most prob- 
ably fitted in the marginal notches mentioned above, that is in such a part of the head 
that their identity with the similar appendages of Pterichthys and Bothriolepis cannot be 
questioned. We may therefore conclude that in Pteraspis, Cyathaspis, Tolypaspis, and Tre- 
mataspis, a pair of prominent oar-like appendages, similar to those in Pteraspis and Bothri¬ 
olepis , was attached to the so called eye notch on the anterior margin of the head. It is 
obvious, however, that if appendages are attached to the first pair of openings in Tremat- 
aspis, ail the remaining eight pairs of openings must hâve been provided with organs of a 
similar nature ! 
This idea, which so completely revolutionizes ail previous conceptions of the structure 
of Tremataspis receives an unexpected confirmation in my recent discoveries in Cephalas- 
pis. For I hâve shown that in the head of Cephalaspis there are indications of the presence of 
a pair of heavy crushing mandibles, so situated that they must hâve acted against each 
other, at right angles to the sagittal plane, instead of parallel with it, as in true Yertebrates. 
Moreover, there are clear indications of the presence of from twenty-five to thirty pairs of 
small jointed and movable appendages extending along the ventral margins of the trunk 
from the head to about the level of the cloaca. That these appendages look like segment- 
ally arranged Arthropod appendages cannot be denied. It seems to me the least that 
can be said is that the burden of proof lies with those who deny they are of that character. 
The argument that it is impossible that an animal so fish-like in appearance should at the 
same time possess many pairs of segmented appendages is not admissible until it is demon- 
strated beyond question that we are dealing with true Yertebrates. No one lias as yet fur- 
nislied any such démonstration. Aside from the crushing mandibles I bave described in the 
Edinburg specimens, nothing is known about the mouth région of Cephalaspis , and it can 
hardly be said that reasonably adéquate pains hâve been taken to learn more about this sig- 
nificant région of an important animal. We are somewhat better off, as far as Pterichthys 
and Bothriolepis are concerued, although the exact location of the mouth is still in doubt, 
and it is not possible to harmonize Whiteaves description of the oral plates of Bothriolepis 
with that of Traquair. We would call attention however to the resemblaiices between the 
