On THE STRUCTURE AND CLASSIFICATION OF THE TrEMATASPIDAE. 
3 
of a whole summer. I considered my self fortunate, therefore, in beiug able to purchase 
almost the entire collection of fossils made by Herr Simonson during that season. The 
collection contained rnany specimens of Thyestes, Gephalaspis and Bunodes, together with 
four heads of Tremataspis , some of which were in exceptionally good condition, but unfor- 
tunately none of the last named genus showed the presence of the plates in the oral région. 
Ail these specimens hâve been added to the collections in Butterfield Museum of Dart- 
mouth College. The material representing the first three généra will be made the subject 
of special memoirs at a later period. 
The four heads of Tremataspis , which hâve been cleaned with great care, enabled me 
to make out several new details concerning the sensory openings on the dorsal surface; tliey 
were the first to show the System of lateral line pits, although these pits were afterwards 
seen on most of the St. Petersburg specimens. But they were of special value, in reconstruct- 
iug the anterior margin of the dorsal sliield, and in discovering the three new marginal 
openings continuing forwards the sériés of six so called gill openings described by Rolion. 
These parts, in the Petersburg material were absent, or had been destroyed by rough 
handling. 
The reconstruction of the oral région was made from a study of the single specimen 
and its cast, that has already been described by Rohon. The original fossil had lost many 
details through repeated handling and the apparently incautious attempts to clean out the 
matrix between the edges of the plates. The original cast, however, was in nearly perfect 
condition, and by taking several impressions of it in dentist’s wax, a beautiful reproduction 
of the original untouched fossil was obtained, from which were worked out ail the details in 
the arrangement of the oral plates shown in the restoration. These casts and the enlarged 
model are now preserved in Butterfield Museum at Dartmouth College. 
t 
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