FROM THE YOREDALE SERIES. ° 625 
portions of the crown are deeply arched downward. The apex of the 
coronal cutting-edge is quite acuminate, much more so than in the 
specimen from Derbyshire figured by Prof. McCoy. Posteriorly the 
crown is very deep, being quite double the anterior face in extent ; 
the largest portion of the posterior coronal surface is occupied by 
a number of broadly expanded imbricating folds of the ganoine 
surface, eight to ten in number. The root is thick, openly porous in 
structure, and, compared with the crown, the root is much con- 
tracted in breadth, 
Whilst the teeth from the Upper Limestones near Leyburn differ 
in so many respects from those of the Lower Limestones of Derbyshire 
and other localities, they possess many characters in common, and 
for the present will ‘be considered as being somewhat modified forms 
of the same species, rather than as representing a separate one. 
Genus Caomartopus, Agassiz, Poiss. Foss. vol. ii. p. 108 (1833) ; 
Worthen, Geol. Survey of Ilinois, vol. ii. p. 31 (1866); Davis, 
Trans. Roy. Dubl. Soc. n. s. vol. i. p. 507 (1882). 
CHOMATODUS LAMELLIFORMIS, Davis, sp.n. (Plate XXVIII. fig. 23.) 
Teeth. Broad in proportion to the height, straight transversely, 
breadth 2 inches, slightly imperfect at one end. Depth of anterior 
face of crown 0°25 inch; depth of base equal to that of the crown. 
Crown thin, cutting-edge acuminate, with a very slight sigmoidal 
curvature ; where not too much worn the cutting-edge is crenulated ; 
it is raised in the centre, and gradually tapers with a circular outline 
to each lateral extremity. Anterior surface of the crown concave, 
bounded by a ridge extending in a straight line across the tooth. 
Ridge prominent, formed by four imbricating folds of the surface. 
Posterior surface near the cutting-edge convex, corresponding to the 
concavity of the anterior surface; lower, towards the base, it is 
concave. Whole surface considerably worn. Base short, thin, equal 
in breadth to the crown. 
This species differs very much from those previously described 
from the massive Lower Mountain Limestone of Britain, such as C. 
linearis, Agass., and C’. acutus, Davis, both of which have been found 
in the limestone near Armagh, and the former also at Bristol and 
Richmond. Chomatodus linearis, Ag., is a broad tooth in compa- 
rison to its height, and does not possess the knife-like cutting-edge 
of C. acutus or C. lamelliformis, Davis. From C. acutus, Davis, 
the present species may be readily distinguished by its great breadth, 
the concayo-convex arrangement of its antero-posterior surfaces, as 
compared with the doubly concave surfaces of C. acutus, its serrated 
cutting-edge, and the greater prominence of the imbricating ridges. 
Genus Pacitopus, Agass. MSS. 
Davis, Trans. Roy. Dubl. Soe. n. s. vol. i. p. 441 (1882). 
Pacrtopus corrucatus, Davis, 0. ¢. p. 444, pl. lili. fig. 25 (1882). 
(Plate XXVIT. fig. 21.) 
