424 WELLBURN : FISH FAUNA OF THE LOWER COAL MEASURES. 
much less numerous, non - denticulated, and smooth. From 
Cte7i acanthus cequistriafus Davis, it seems more widely separated, 
the shape being different and also the direction of the ridges, 
which in C. cequistriafus Davis, besides being more numerous, 
run longitudinally parallel with the anterior margin, with the 
result that they die out along the latero-posterior margin"^ without 
inosculation, w^hich is not the case in the present specimen. 
From the other spines of this genus it seems to be still more 
widel}^ separated. 
Characters. — Total length 90 mm., but the spine being 
broken across just below the commencement of the inserted 
portion, the original length was probably about 110 mm. Length 
of posterior border to commencement of inserted portion 75 mm., 
of anterior border to same point 90 mm. Diameter at com- 
mencement of inserted portion 15 mm., from this point the spine 
gradually narrows to a moderately fine point. Lateral surfaces 
meet in front at an acute angle : the ornamentation consists of 
smooth straight ridges which, at a point half way between the 
tip and commencement of the inserted portion, number seven, 
but between this point and the base the number is increased 
by intercal cation to nine. The ridges are divided from one 
another by spaces about equal to their diameter. Their direction 
is also very characteristic ; the most anterior one forms a keel 
on the anterior border, the next four run to the tip parallel 
with that border. The most posterior ridge runs parallel with 
the posterior border, while another runs between these two sets 
towards the point where they meet in front, and, lastly, on 
each side of this ridge are two shorter ones. The posterior 
surface is concave from side to side, and where it meets the 
lateral surface is armed by a row of well marked beak-shaped 
denticles, which are separated from one another by a distance 
about equal to their diameter at the base. Anterior to these 
denticles on the lateral surface and posterior to the most 
posterior ridge is a second row of nine small, more-rounded 
iSee Quart. Jouni. GeoL kSoc, vol. xxxv, pi. x. 
