FROM THE YOREDALE SERIES. 621 
more or less curved or bent over towards one side, a feature which 
may be seen in the example figured. The base is strong and fibrous, 
and extends backwards from the crown in a horizontal position. 
It possesses very similar characters to the base of the teeth of 
Cladodus, and has probably been attached to a cartilaginous jaw, 
in the same manner as the teeth in that genus were. 
PRIsTICLADODUS concrINNvs, Davis, Trans. Roy. Dubl. Soc. n.s. vol. 1. 
p. 385, pl. xlix, fig. 23 (1882). (Plate XXVI. fig. 15.) 
This species is very rare. It is easily distinguished from P. den- 
tatus, McCoy, by the acutely prolonged upper extremity of the crown, 
by the lateral denticulations, which are acuminate and small 
compared with the semiglobose and rounded denticulations of 
P, dentatus. 
Genus GuypHanopus, Davis, Trans. Roy. Dubl. Soc. 
n. 8. vol. 1. p. 386 (1882). 
The teeth referred to this genus are extremely thin and slender, 
and possess characters which appear to indicate an intermediate 
form between the Cladodonts on the one hand and the Petalodonts 
on the other. By the acuminate apex of the crown and its sharp 
cutting-edge they are closely related to the former; whilst the root is 
devoid of the broadly expanded, more or less horizontally extended, 
base of the Cladodonts, and descends vertically, to an equal depth, 
in many cases, te the height of the crown, and in this respect 
they approach the Petalodonts. 
GLYPHANODUS TENUIS, Davis, l. ¢. p. 386, pl. xlix. figs. 24, 25 (1882). 
(Plate XXVIT. fig. 8.) 
The base extends downwards from the crown, varying in depth, 
generally equalling or exceeding the height of the crown. It is 
thin and laterally coextensive with the base of the crown. 
The several teeth referred to this species vary slightly in form, 
whilst agreeing in the principal characteristics. Examples are 
occasionally met with in which the posterior. surface is not only 
laterally concave, but they are vertically concave, the apex of the 
crown having a decided flexure backwards. The majority of the 
teeth are straight between the base and the summit of the crown ; 
the latter is frequently much reduced by attrition, the sharp point 
giving place to a more or less rounded margin. 
Genus Prratoporsis, Davis, Trans. Roy. Dubl. Soc. 
n. s. vol. i. p. 498 (1882). 
The genus Petalodopsis, as its name indicates, bears a close rela- 
tionship to Petalodus; but whilst in its general characters it 
nearly approximates to that genus, it exhibits striking divergences in 
several minor points. The cutting-edge of the crown is deeply 
divided into three large and pointed denticles, the centre one being 
the most prominent and rendering the outline more or less tri- 
