40 Dr. R. H. Traquair on the 
from the closure of the sulcus, and only marked by delicate 
longitudinal strie, while in one I find it devoid of tubercles 
along its whole extent. In some too, before the truncation of 
the apex occurs, the gyrating ridges tend to lose their close 
tuberculation, at least posteriorly, and to become only distantly 
nodulose or even quite plain. 
Putting the wearing of the tips altogether aside as a secon- 
dary question, the striking want of bilateral symmetry in 
these spines, together with their occurrence in “rights and 
lefts,” amply justifies the opinion of Messrs. Kirkby, Atthey, 
and Hancock that they were pectoral or at least paired appen- 
dages. Which are the right and which the left spines it is, 
however, at present not very easy to determine. Accepting 
the suleated aspect as posterior, it would be necessary to 
ascertain whether the flat or the gibbous side was superior in 
order to indicate to which side of the fish it belonged. 
Now, turning. to the spines labelled ‘‘ dorsal” in the same 
collection, we find that they are smaller in size, varying in 
length from 44 to 10} inches, and almost all lying laterally 
compressed on pieces of shale. In this way the lateral cur- 
vature is obscured, though in one, also marked “ dorsal,” 
which happens to be only obliquely placed on its matrix, this 
curvature is quite obvious. Furthermore, all of them show 
in other respects the same want of lateral symmetry which 
I have just described in those acknowledged to be pectoral, 
namely the possession of a flat and of an inflated and grooved 
side ; in fact they are rendered still more asymmetrical than 
the large truncated spines by the much greater prominence 
and sharpness of the posterior marginal keel, which we have 
seen is morphologically a lateral structure in the general plan 
of the spines. This keel is also furnished with a row of small 
closely-set recurved denticles. The gyrating ridges become 
very oblique towards the point, and tend to become plain or 
only distantly nodulose, except perhaps on the front of the 
spine. On the flat side a space bare of ridges runs down from 
the point along the posterior margin for about 14 inch, and 
an analogous appearance is also observable on the grooved 
side. The groove itself is smooth and marked with delicate 
longitudinal striz ; and, as Messrs. Hancock and Atthey have 
already noted, the point is much compressed laterally*. 
If we next compare the proximal or basal end of one of the 
* These young spines of G. tuberculatus bear an extreme resemblance 
to the figure of G. denticulatus, Davis, in Ann. & Mag. Nat. Hist. (5) vi. 
1880, p. 373, being similar in shape, in the characters of the gyrating 
ridges, and the denticulation of the posterior margin, while the same bare 
space runs down fora little distance from the point. Myr. Davis, how- 
ever, states that his spine has ¢wo rows of denticles posteriorly. 
