632 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 22, 
in connexion with these columns, which seem to divide into their 
component parts as they approach them, two or three being thus 
joined to each column; but in all our specimens this part of the fish 
is injured. The lateral plates are narrower than those lower down 
the body, and apparently gradually subside into the columns, without 
any distinguishing point. 
These lateral plates at this point incline forwards; the few next 
lower down are much inclined backwards; so that there is here a 
large space over the abdominal region devoid of all such appendages. 
In all the four specimens this is the case, as well as in the German 
specimens before referred to ; and it is therefore probably the natural 
condition, and is not owing to accidental circumstances, though it is 
possible enough that pressure may have had something to do in 
forcing the plates asunder. 
The ventral plates (m) extend from the root of the ventral fins to 
almost the commencement of the anal; and from the lower part of the 
posterior plate there is a stout rod or process (0) extending upwards 
and backwards as far as the outer extremities of the lateral plates. 
Below, this process is wide and flattened ; above, it is cylindrical ; and 
at the point where this change takes place it is obtusely angulated 
backwards, the whole being a little arched in the same direction. 
There are apparently two of these great abdominal rods or processes, 
one belonging to each side, giving support probably to the lower 
posterior boundary of the abdominal walls and limiting in this di- 
rection the naked space above alluded to as extending over the lateral 
walls of the abdominal chamber. These two stout rods are closely 
pressed together, and in all the specimens are much confounded with 
each other. 
Above the median line, in front, the outer members of the series of 
transverse plates and rods are likewise considerably modified. The 
change takes place gradually, just behind the elevated portion of the 
dorsal fin. The lateral plates (fig. 3, g), however, are only slightly 
modified ; but instead of being united to rods are continued as broad 
flat plates (7), which, inclining forwards, become angulated in front, 
and then for a short distance (7) incline backwards and are united 
to a series of hour-glass-shaped plates (4) that lean in the opposite 
direction, are extended to the dorsal margin, immediately below the 
anterior portion of the dorsal fin, and form part of an extended series 
that reaches to the root of the tail. The broad plate inclining for- 
wards and in continuation of the lateral plates, is undoubtedly a modi- 
fication of the rod of the posterior part of the body ; its margins are 
abrupt and produced into slightly elevated ridges ; and it contracts a 
little towards its outer extremity, and is slightly thickened at this 
point. The next portion, which inclines backwards, appears to re- 
present the sigmoidal ridge or plate. The margins of this portion 
of the series are in contact, and seem to be slightly imbricated ; and 
the outer extremities are turned a little forwards to become united 
to the external hour-glass-shaped plates. 
In the transverse centre of these modified sigmoidal plates there 
is a ridge (7), similar in appearance to that on the median lozenge- 
4 
