506 On the Fossil Fishes of the Carboniferous Limestone Series of Great Britain. 
It was remarked, when describing P. elongatus, that one portion of the teeth 
have an anterior coronal surface which is convex, whilst another is concave along 
the same area. Some of the teeth belonging to the genus now being described 
exhibit the same peculiarity. Their general resemblance in other respects almost 
precludes the possibility of their being different species. They have about the 
same number of radicles to the roots; the posterior aspect of the tooth is the same 
in both, and the peculiar development of the ductJike marking on the anterior 
basal region is exactly the same in each. The anterior portion of the crown, how- 
ever, offers several peculiarities differing in the two. The anterior coronal surface 
is concave, and more compressed along the crest, producing a very sharp cutting 
edge, slightly crenulated. ‘The anterior median ridge is more prominent, and con- 
stittites an acute angle with the upper basal area; and it is devoid of the band of 
enamel which stretches across the teeth already described. It appears probable 
that these were teeth from the upper jaw ; whilst those with a convex crown have 
been derived from a lower jaw. As to whether there were several of the teeth form- 
ing concentric rows, as in the sharks, or whether they were arranged otherwise, 
there is no evidence, except the general character of the teeth, to show. 
This species possesses characters which separate it from all others hitherto 
described. Its long, pectinated appearance and the number of its radicles, easily 
distinguish it. The one nearest resembling it is P. piasensis, St. J. & W. (“ Geol. 
Sury. Illinois,” Vol. VL, p. 386, pl. 13, fig. 12), it is little more than half the size, 
and possesses only nine or ten radicles. 
Formation and locality : Mountain Limestone, Armagh. 
Ex coll. Earl of Enniskillen. 
Polyrhizodus constrictus, Davis. 
(EL, JWG, itttee, 11) 
Teeth, crown very small in comparison to the base or root. Greatest diameter 
of crown 11 inch; diameter of root along the same plane, 1°65 inch; depth of 
tooth from the surface of crown to bottom of roots, ‘75 of an inch, The crown is 
narrow from back to front, not more than ‘3 of an inch, smooth, and its central por- 
tion, much worn by trituration, rises at a slight angle from the anterior ridge to the 
crest ; lateral extremities much raised ; surface falling from each end towards the 
centre, and forming a deep concavity ; anterior ridge continuous with the crown of 
the tooth without demarcation, but stands boldly forward above the narrow inter- 
basal area ; ornamented by four or five imbricating folds of the ganoine, by which 
it is covered ; posterior surface partially imbedded in the matrix. It extends from 
the slightly rotund coronal crest to form a junction with the rootlets, and is not 
marked by any very distinct posterior ridge. The roots are large, tuberculous, 
broader than the crown of the teeth from back to front ; the largest in ceutre °45 
of an inch in diameter. The rootlets towards each end of the tooth are smaller; 
