186 J. W. DAVIS ON FISH-SPINES FROM 
of the exposed with the imbedded part of the spine is 58, of an inch, 
measured at right angles to the length. From this point to the apex 
the width diminishes gradually in the lower and middle portions of 
the spine; but the margins converge more rapidly in the upper part, 
and the spine ends in an acute point. The base, which presents the 
usual fibrous structure, tapers rapidly to a roundish extremity and is 
conical in form. The spine is compressed laterally ; but on account of 
its being imbedded in the matrix, the form of a transverse section 
cannot be ascertained. The exposed side is ornamented with a series 
of evenly parallel ridges. There is no appearance of the anterior 
outline being produced to form a carina. Near the base the ridges 
are thirteen in number; they run longitudinally parallel with the 
anterior margin of the spine, the result being that they die out or 
disappear along the latero-posterior margin without inosculation. At 
the apex, only the two most anterior ridges remain and form a fine 
point. The ridges are narrower than the intermediate furrows, and 
are divided along their summit into minute papilla-like tubercles, 
which are tipped with ganoine. The posterior angle does not appear to 
be very thick. Itis armed along the entire length of the exposed part 
with numerous small obtuse denticles separated from each other by 
about their own diameter ; they differ from the posterior denticles 
of C. hybodoides, Eg., in being quite dissociated from the ridges. 
The spines of Ctenacanthus to which this one bears the greatest 
resemblance are those of C. denticulatus of M‘Coy*. There is, how- 
ever, considerable dissimilarity between the two forms; C’. denticulatus 
is longer in proportion to its breadth, and much more elongated to- 
wards the apex. The ridges run parallel with the dorsal margin of 
the spine as well as the anterior, the intervening ones being pro- 
duced by bifurcation. The sides of each ridge are denticulated with 
sharp recurved teeth extending halfway across the intervening spaces, 
the denticle on one side being connected with that on the other by 
a slightly oblique fold across the ridge. The denticles along the 
latero-posterior angles are larger and more pointed. 
I haye delayed the description of this Ichthyodorulite for: some 
time in the hope that some other specimens might be found ; but 
none haying been added to my own or other collections, I think the 
characters of this specimen sufficiently clear and distinct to warrant 
its addition as a new species, and propose for it the name C. equi- 
striatus. 
PHRICACANTHUS } BISERIALIS, n. gen. et sp, (Pl. X. figs. 16,.17.) 
Spine of medium size, about 4:3 inches in length; its greatest 
diameter is ‘3 inch. It curves gently backwards. The exposed 
part is covered by minute longitudinal striations; the furrows 
slightly broader than the ridges and minutely pitted at their base. 
An internal cavity, circular in form, extends from the base nearly 
the whole length of the spine. The opening at the basal end appears 
* «British Paleozoic Rocks and Fossils,’ by Sedgwick and M‘Coy, p. 256, 
pl. ii. K. fig. 16. 
t From ¢pié, a ripple, and d«cayOa, a thorn, 
