340 On the Fossi! Fishes of the Carboniferous Limestone Series of Great Britain. 
anterior surfaces are much compressed and ornamented by numerous longitudinal 
ridges ; very small and separated by furrows their own diameter in width. Both 
the ridges and furrows are largest near the base, towards the apex of the spine they 
decrease considerably in size especially along the posterior margin, into which they 
are ultimately absorbed and disappear. The furrows are deep in proportion to their 
width ; there are about forty on each side. Transversely across the ridges there 
extend minute plica or folds, these are continued down each side of the ridge and 
join, at the base of the furrow, a similar fold from the side of the opposite ridge. 
Each separate ridge has the appearance of a long string of minute cups the narrow 
base of each being placed in the extended mouth of the one preceding it, and when 
highly magnified presenting an extremely beautiful appearance. ‘The anterior face 
of the spine is slightly rounded but accuminate and is not characterized by any 
peculiarity in the ridges which continue to cover it. A wide and deep open cavity 
occupies the lewer posterior portion of the spine ; about equidistant between the 
base and apex this becomes enclosed and extends far towards the latter. The 
enclosed cavity is very large and the sides of the spine forming its walls are pro- 
portionately thin. The teeth extending along the postero-lateral angles are not 
preserved with sufficient distinctness to be described, though the broken stumps 
are distinguishable, the teeth having been broken away with the matrix. 
The ornamentation of the ridges of this species bears a slight resemblance to 
that of C. crenatus, Ag., or C. denticulatus, M‘Coy. In the former the crenulations 
are formed by a row of small transverse tubercles extending obliquely down the 
sides of the ridges and rarely passing over its summit, whilst in C. denticulatus the 
sides of the ridge are denticulated with sharp recurved teeth extending half 
way across the intervening holiow, and slightly connected across the ridge. The 
characters of both are sufficiently distinct from the species now described, even if the 
general form of the spine was less distinct in each case, whilst near the same length 
as C.denticulatus, it is double its breadth, and there are considerably more than double 
the number of ridges on each lateral surface. Ctenacanthus speciosus, St. John 
and Worthen (‘Geological Survey of Illinois,” Vol. VI., p. 424, pl. xiv., figs. 
3, 4), appears to be closely related to this species. It may be distinguished by 
the lateral striation being closer, with narrower interspaces, and the transverse 
ornamentation of the ridges not extending so far across the intermediate furrow. 
Locality : The specimen described is from Oreton in Salop. Specimens have also been found at Bristol 
which possess the same characters and are without doubt the same species ; they are, however, of a some- 
what stronger and more robust appearance than the Salopian specimens.—AIl are from the Mountain 
Limestone. 
fie coll. Karl of Enniskillen. 
Ctenacanthus dubius, Davis. 
(EM, SOLEog sie, %e)) 
A spme 2°5 inches in length, and ‘5 of an inch in greatest breadth. Slightly 
curved on the posterior margin, considerably more so on the anterior one. The 
