On the Fossil Fishes of the Carboniferous Limestone Series of Great, Britain. 481 | 
is greater than the longitudinal ; but all approximate, more or less, to a right- 
angled outline. 
Formation and locality ; Mountain Limestone, Armagh. 
Ex coll. Earl of Enniskillen. 
Mylacodus sesamini, Agass. MSS. 
(IPL, IWAQUL., tikes BBs) 
Teearadtes sesamini, L. Agassiz, 1859. MSS. in the Enniskillen Coll. 
5 5 Enniskillen, 1869. <“‘ Cat. Type Specimens,” p. 7. 
Teeth ; length, ‘6 of an inch, breadth, °7 of aninch. Crown, longitudinally convex, 
worn by attrition on the anterior portion. Transversely, the central part is ele- 
vated and flat. A considerable depression extends along each side the central 
elevation, from which the surface again rises to form rather prominent lateral 
borders. Coronal surface, enamelled, minutely and uniformly pustulately rugose. 
The anterior margin is slightly convex, lateral ones having a slight convexity. 
The posterior margin is deeply convex. All the angles are obtusely rounded ; 
only a single specimen has hitherto been found ; the base is hidden by the lime- 
stone matrix. 
This species may be distingushed from M. quadratus by its more cone-shaped 
form, and the decidedly rugose markings on the coronal surface. 
The palate in the collection of the Earl of Enniskillen, named by Prof. Agassiz 
Pinacodus sesamini, differs materially from the type of that genus. Its quadrate 
form, rounded angles, and the arrangement of the coronal surface, separate it dis- 
tinctly from the type of the genus Pinacodus. At the same time they indicate, 
with equal certainty, its relationship to Mylacodus. I have, therefore, placed it in 
the latter genus, retaining the nomen triviale, sesamini of Agassiz to distinguish it 
from Mylacodus quadratus, Agass. 
Formation and locality : Mountain Limestone, Armagh. 
Ex coll, Karl of Enniskillen. 
Genus.—Homalodus, Davis. 
Palatal teeth; outline more or less quadrate or trapeziform, medium 
size, thick and strong. Crown flat, lateral extensions unequal; coronal surface 
enamelled, punctate, or reticulated ; anterior margin, convex or straight ; lateral 
margins straight on one side, the other conyex; posterior margin more or less 
sinuous. One of the postero-lateral angles forms a considerable expansion from 
the coronal surface, terminating-in an acute angle. Base thick, slight convexity in 
medium area of transverse section, concave on each side, longitudinally straight— 
conforms generally in outline to that of the crown, smooth, fibrous. 
The flat, pavement-like coronal surface of this species, combined with its irre- 
gular contour, and the one-sided horn-like prolongation of the postero-lateral angle, 
serve to render its character sufficiently peculiar, and to distinguish this genus 
from all others, 
: 4K 2 
