382 THE AMERICAN NATURALIST. [Vor. XXXVI. 
good condition; but, unfortunately, none of the last-named 
genus showed the presence of the plates in the oral region. 
All of these specimens have been added to the collections in 
Butterfield Museum of Dartmouth College. 
The four heads of Tremataspis (which have been cleaned 
with great care) have enabled me to make out several new 
details concerning the sensory openings on the dorsal surface; 
they 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 
that they enabled me to work out the structure of the anterior 
margin of the dorsal shield and to discover three new openings 

Fic. 3. — Head of Tremataspis seen from the side. 
in the series of so-called gill openings described by Rohon. 
These parts in the Petersburg material were absent or had been 
destroyed by. rough handling. 
The reconstruction of the oral region was made from a 
study of the single specimen and its cast that have 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 mold, however, was in nearly perfect con- 
dition, 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 all the details in the 
arrangement of the oral plates shown in the restoration. 
These casts and the enlarged model are now — in 
Butterfield Museum at Dartmouth College. 
Our observations on the structure of Troinatipis have 
brought out the following principal facts: 
The Lateral-Line Organs of Tremataspis consist of a series 
of shallow groove-like dots and dashes, arranged in linear 
series on the dorsal surface of the shield. We distinguish a 

