FISH OF THE CARBONIFEROUS PERIOD. 11 



Ctenacanthus denticulatus (M^Coy). 



Sp. Char. Spine nearly straight, slightly curved towards the 

 apex ; length of naked portion 5| inches, length of the rapidly 

 tapering base 2 inches, width near base 9 lines ; section trun- 

 cato-elliptical, sides slightly convex, front narrow, rounded ; 

 posterior face wide, depressed, concave at both sides, with an 

 obtuse ridge in the middle, the lateral angles closely set with a 

 row of numerous small, conical, downward- curved teeth on each, 

 their own length apart ; longitudinal ridges rounded, less than 

 their own diameter apart (about four in two lines in the mid- 

 dle of the ray), they are a little wider at base than towards the 

 apex, increasing in number downwards by dichotomy; the 

 sides of each ridge are denticulated with sharp, recurved teeth 

 extending halfway across the intervening spaces, the denticle 

 of one side connected with its fellow on the other by a slightly 

 oblique fold across the ridge, each pair being separated from 

 that above and below by about the thickness of the ridge ; 

 near the posterior margin on each side are four or five ridges 

 much smaller than the rest, crossed by oblique blunt tubercles. 



This species slightly resembles the C. crenatus (Ag.) in its 

 ornament, but instead of the short, close notches in the sides of 

 the ridges of that species, this is distinguished by the more di- 

 stant, tooth-like denticulation and narrow transverse plicae. 



Not uncommon in the dark shale (of the age of the yellow 

 sandstone) of MonadufF, Drumlish, in the N. of Ireland. 



{Col. University of Cambridge and Mr. Griffith.) 



Ctenacanthus distans (M'Coy). 



Sp. Char. Spine compressed, gently arched, very long, slender, 

 tapering at the rate of only 8 lines in 5 inches ; posterior face 

 with two rows of numerous small, short, conical compressed 

 teeth, slightly bent downwards, rather more than the width of 

 their base apart ; sides flattened with about ten or twelve close 

 flattened longitudinal ridges of irregular width, the broadest 

 occasionally subdividing as they approach the base, all the ridges 

 crenulated by small tubercles, about double the thickness of 

 the ridge from each other ; those on the anterior ridges are 

 transverse and slightly oblique, while those nearer the concave 

 margin are smaller, and assume the appearance of lengthened, 

 nodular swellings, as in Physonemus. 



This is a remarkably long and slender ray; one specimen in 

 the University collection at Cambridge, of which a considerable 

 portion of the apex must be lost, measures six inches in length 

 and only six lines in width at the broadest part near the base. 



