On THE STRUCTURE AND CLASSIFICATION OF THE TfiEMATASPIDAE. 
9 
The original fossil was so badly worn by repeated handling and imskillful attempts to 
rernove tbe matrix, that mucli of its former character was lost. On tbe other liand the 
original cast was in a practically undisturbed condition, so tbat onr wax impressions of it 
gave a perfect reproduction of tbe untouched fossil. I liope to bave tliese impressions re- 
produced by photographs, so that the exact basis of the reconstructions will be accessible. 
I recognize in tbe oral région one unpaired, triangulär plate; four rows of large paired 
ones; and a row of four or five small plates just back of the anterior margin of the dorsal 
shield. Tbe latter is badly crushed and it is not possible to make out its original condition witli 
certainty. I bave given on the left side an exact représentation of tbe plates seen in tbe fossil. 
Tbe marginal plate of tbe first row, not counting tbe row of small square plates, is 
almost certainly a distinct plate, but whether the other pièces in thisrow are distinct plates, 
or fragments of a large crushed one, could not be determined from tliis fossil. It is very 
probable tbat a large isolated plate figured by Rolion ’93, (PI. I. fig. 2.) and which most 
probably cornes from tbe oral région of Tremataspis , belongs in tliis row. It fits fairly well 
into the place filled by tbe crushed fragments, and tbere is apparently no other place in tbe 
oral région for such a large plate. Tbis plate, however, cannot be tbe isolated «mittlere 
Seitenplatte» as R о bon daims, for in tbe cast under considération, tbe two plates lie nearly 
side by side, and the différence in size and form between tbem is very striking. Tbis large 
plate appears to be movable or to bave bad some movable body attacbed to it, for it has at 
one end a small rounded notch or joint. A détermination of whether tbis notcli was at the 
médian or lateral end of tbe plate would probably throw a great deal of light on tbe meaning 
of ail the oral plates. 
If three plates were present in tbis row, instead of two, as shown on tbe right side of 
tbe model, the joint between tbe first two plates would corne opposite tbe one between tbe 
first two plates of the second row. On tbis supposition, however, there would be no place 
for the large notched plates, unless tliey were placed lengthwise of tbe liead so that the 
tooth-like process on tbe dorsal shield could fit into the notch on tbe ends of tbe plates. 
Tliis, however, would bring tbem into an unnatural position, overlapping the median plate 
and part of tbe first two rows. 
Moreover, if the plates are left as tliey are in my restoration, they correspond roughly 
witli the two large mandibular plates of Pterichthys. Traquair figures an incision on tbe 
lateral margin of tliese mandibular plates tbat is supposed to be a nasal opening. But it is 
hardly probable tbat tbe notch at the end of tbe plate in Tremataspis can bave tbis 
significance. 1 ) 
1) If this plate is placed transversely, as in the figures, 
and with its notched end next the margin of the oral 
région, the notch would fall in line with those on the poste¬ 
rior marginal plates and would add still another marginal 
opening to the nine already known. If we adhéré to our 
interprétation of these openings, this would mcan the 
Зав. Физ.-Ыат. Отд. 
presence of a pair of small antenna-like appendages, just 
in front of the pair of large oar-like swimming ones. 
However the position of this plate is as yet so doubtful 
that we do not attach too much importance to such a 
spéculation. 
2 
