344 On the Fossil Fishes of the Carboniferous Limestone Series of Great Brituin. 
portion of the posterio margins. Dr. Buckland also stated in a manuscript des- 
cription of the spine that there appeared on its posterior surface, two rows of regular 
tubercles. Prof. Agassiz considers that the denticles may be merely due to the 
termination of the longitudinal furrows. After some hesitation, however, he placed 
the spine in the genus Onchus, at the same time recognizing its resemblance to 
Hybodus. 
After careful study of specimens, there appears sufficient evidence of posterior 
denticles ; and the close resemblance, and evident relationship to the species forming 
the genus Ctenacanthus, renders necessary its removal to that genus. 
This species bears some resemblance to C. levis and C. plicatus, from the latter it 
will be distinguished by its greater breadth and its greatly compressed oval section, 
and from the former by the longitudinal ridges on each side, which in C. devs run 
parallel with the posterior margin and in C. sulcatus with the anterior one. 
Formation and locality : Carboniferous Limestone, Bristol. 
Ex coll. Bristol Museum. 
Ctenacanthus pustulatus, Davis. 
(Pl. XLV., fig. 2.) 
Length of spine nearly four inches, greatest width at the base of the exposed part 
‘5 of aninch. The spine is slightly curved, the anterior border more so than the pos- 
terior. The base extends 1'4 inches along the posterior border, and 1-2 of the anterior 
one is occupied by it. The remaining portion of the spine contracts gradually toa 
point and is covered with longitudinally arranged strize, most numerous at the base 
of the exposed portion and diminishing in number towards the apex, not by anasto- 
mosing but by the gradual thinning out and disappearance of the ridges The 
surface of the strize or ridges is coated with ganoine and is quite smooth ; along the 
posterior part of the spine they are about the same diameter as the intermediate 
hollows, but near the anterior portion the hollows occupy a greater space than the 
ridges. The hollows are covered by numerous pittings arranged in longitudinal 
rows parallel to their own direction, and there are also in the most anterior ones 
several detached ganoine-tipped pustules rising to a level with the ridges, The 
lateral surface is slightly compressed, rather more so towards the posterior border. 
Along the whole length of the posterior margin there is a double row of hooks or 
small denticles, broad at the base, culminating in an obtuse point. 
Locality : Mountain Limestone of Armagh, 
Ex coll. Karl of Enniskillen. 
