434 On the Fossil Fishes of the Carboniferous Limestone Series of Great Britain. 
forming an angle of 5C° with the outer edge, the anterior part of which forms the 
third ridge ; the secondary ridge is more obtuse than the other two, and a little on 
the posterior side of the middle, the intervening spaces deep, concave. Entire 
surface, minutely granulo-punctate, by the extremities of the vascular canals 
(averaging eight in one line), covered in some places with a very thin layer of 
ganoine. Average length of posterior tooth one inch two lines, width at anterior 
margin eight lines, length of anterior tooth seven lines, width of posterior margin 
six lines.” 
In the above description Prof. M‘Coy, describes each ramus of the jaw as con- 
sisting of three teeth and describes two of them, the posterior and anterior ones ; 
the middle tooth being unknown. By a careful comparison of the teeth, which 
form a very numerous suite, in the Enniskillen Collection, it has been found that 
they may be naturally and easily divided into four groups, viz., the right and left 
teeth of the upper jaw (M‘Coy’s anterior teeth) and the right and left teeth of the 
lower jaw (called by M‘Coy, posterior teeth). The former described by Prof. 
M‘Coy, as seven lines in length, average in the Enniskillen Collection 1:25 inch, 
and several examples are more than 2 inches in length, and 1°5 inch across the 
posterior margin; a larger size than is exhibited by the opposing teeth of the 
lower jaw. The triturating surfaces of the teeth by the arrangement indicated 
above correspond one to the other ; the hollow of the upper tooth corresponding 
to the projections or ridges of the lower one, and vice versa ; this is especially the 
case in some of the larger specimens, whose surface is much worn, and considering 
that it is quite impossible to ascertain the actual teeth which pertained to any 
identical fish, the worn surfaces fit very accurately to those of the opposing jaw. 
The teeth are strong and thick; in large and well developed specimens the 
thickness is equal to half the width. Anteriorly, the tooth is comparatively thin, 
it increases in thickness towards the posterior and median portions and as is the 
case with other Cochliodonts it is probably in this direction that the tooth has 
increased in size, the growth being along the posterior edge. 
Prof. Owen, in the Geological Magazine (Vol. IV., p. 62, pl. iv., fig. 1), describes 
a tooth from the Limestone of Yorkshire, at present in the Woodwardian Museum, 
Cambridge, as Cochliodus compactus “‘the predominance of the middle over the 
posterior and anterior lobes giving the guiding surface of the tooth a more compact 
and simple character.” It is an example of Deltoptychius acutus, Agass., and as 
the latter name has priority, C. compactus, Owen, can only be retained as a 
synonym. 
Formation and locality ; Mountain Limestone, Armagh. 
He coll, Karl of Enniskillen. 
