422 On the Fossil Fishes of the Carboniferous Limestone Series of Great Brita. 
fine granulo-punctate by the opening of the medullary glands, average length 
of posterior tooth, one inch five lines, greatest width eight lines, width of middle 
tooth five lines.”—-(1/‘Coy.) 
The Enniskillen collection is extremely rich in the number and beauty of the 
specimens of Cochliodus contortus. ‘Two specimens exhibit the teeth of the right 
and left ramus of one jaw in natural position. They are represented on Pl. LIL, 
figs. 1,2. Figure 2 a, represents the posterior tooth and 2 6 the second tooth, of Prof. 
M‘Coy’s description. The anterior teeth still remain unknown. A very careful 
examination of the specimens of single teeth as well as the more perfect ones alluded 
to above, and a pair of teeth in the Jones’ Collection at the Geological Society of 
London, has failed to show any trace of teeth anterior to those shown in the figures, 
nevertheless the anterior margins of the second teeth of M‘Coy appear to end ab- 
ruptly and incompletely, and until more conclusive evidence be obtained, it may be 
better to withhold any opinion as to their occurrence or otherwise. The cartilaginous 
mass of the jaw supporting the teeth is preserved in some specimens, (see PI. LIL, 
figs. 1 and6). In Pl. LIL., fig. 1 it extends vertically parallel with the inside of the 
jaw, and is about an inch in thickness. Pl. LIL, fig. 6 represents a smaller tooth, 
and in this case also it will be seen that the jaw extends considerably beyond the 
outer or inrolled margin of the teeth and is expanded into a broad, thin, plate-like 
mass in which the teeth are embedded. 
Prof. M‘Coy has asserted that teeth of Cochliodus (Streblodus) oblongus, Ag., 
have a ‘‘ vertical mode of succession, the young one being distinctly visible beneath 
the level of the old one (‘‘ Brit. Paleoz. Foss.,” p. 623, pl. 3 L., fig. 28, and pl. 3 H., 
fiz. 19) from a transverse fracture” ; “the fractured edge shows the inrollment 
of the outer margin of the tooth, and the whole thickness of its substance, showing 
the vertically tubular structure of the superficial half, and the two dense layers 
which form its concave under or dorsal surface. At about the thickness of the 
substance of the old tooth lower down is seen the young tooth, exactly concentric 
to it in outline and having its structure similarly displayed in the section.” Speci- 
mens occur in the collection of Lord Enniskillen, which were prepared by the late 
Mr. Crawford, his lordship’s assistant in the museum, with great delicacy and care ; 
and these exhibit with perfect clearness the manner in which the teeth of the Coch- 
liodonts grew or increased in size. Pl. LIL, figures 4 and 6 represent respectively the 
larger and smaller teeth, from which it will be seen that the teeth on their initiatory 
stages were very small, and that they constantly and persistently increased in size 
by the addition of dentigerous matter to the inner margin of the dental surface, 
causing the helicine form of the section and the convoluted contortion of the surface 
of the tooth. As the growth of the tooth increased its size, doubtless corresponding 
with the growth of the fish, the earlier or outside convolutions became embedded 
in the cartilagmous mass of the jaw. It is an internal convolution of this kind 
which, having become detached from the main mass of the tooth, deceived Prof. 
