Pisces. ] UPPER PAL/EOZOIC VERTEBRATA. 625 
CTENACANTHUS DENTICULATUS (M/°Coy). PI. 3. K. fig. 16. 
Ref —M°Coy, Ann. Nat. Hist. 2nd Series, Vol. II. p. 116. 
Dese.—Spine nearly straight, slightly curved towards the apex; length of naked portion five and half 
inches, length of the rapidly tapering base two inches, width near base nine lines; section truncato-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 middle 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 half way 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 distant, tooth-like 
denticulation and narrow transverse plicze. 
Position and Locality—Not uncommon in the dark shale (of the age of the yellow sandstone) of Mona- 
duff, Drumlish, in the North of Ireland. 
Explanation of Figures—P1. 3. K. fig. 16, dorsal spine natural size, from the yellow sandstone shale 
of Monaduff; fig. 16 @, ditto, some of the ridges near the anterior face magnified. 
CTENACANTHUS DiIsTANS (A/‘°Coy). PI. 3. K. fig. 15. 
Ref—MCoy, Ann. Nat. Hist. 2nd Series, Vol. II. p. 116. 
Desc.—Spine compressed, gently arched, very long, slender, tapering at the rate of only three lines 
in five 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 nodulose swellings, as in Physonemus. 
This is a remarkably long and slender ray; one specimen in the University Collection, 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, the broken distal extremity being three lines wide, which would pro- 
bably indicate a further inch and half of length. The portion of the base inserted in the flesh is small 
and gradually tapering. I am not certain of the exact form of the section. 
Position and Locality —Not uncommon in the red limestone of Armagh. 
Explanation of Figures.—P1. 3. K. fig. 15, dorsal spine natural size, imperfect at the tip, shewing the 
elongate tapering base of insertion and internal cavity in lower part; fig. 15 a, ditto, portion of surface 
magnified, shewing the variable width and mode of tuberculation of the ridges. 
CTENACANTHUS HETEROGYRUS (Ag. name only). PI. 3. I. fig. 32. 
Desc.—Very short, rapidly tapering ; length of exposed portion two inches three lines, at which length 
it forms an obtuse point from a width at base of five lines (measured at right angles to the length), very 
slightly arched, the posterior outline nearly straight, the anterior one convex. Sides flattened, converging 
to the narrow anterior face, which is occupied by a flattened smooth ridge, about twice as wide as those 
of the sides; lateral ridges extremely irregular in size, shape, and marking; rather thick, separated by 
deep sulci less than half their width; ridges averaging four in two lines at four lines in diameter, some 
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