EXPLANATIONS OF PLATES. 
PLATE XV. 
Fig. 1. Shell of Bothriolepis canadensis Whiteaves, from above. 
(From Whiteaves 
Fig. 2. Anterior part of same, from below. (From Whiteaves.) 
Fig. 3. Skull of Mycterops ordinatus Cope, from below, # natural size, 
PLATE XVI. 
Cast of brain-case of Diadectes sp. 
Figs. 1 and 2, cast of cranial cavity, natural size. As the basicranial 
axis is lost, the inferior outline posteriorly is provisional only. 
Fig. 1, from above 
Fig. 2, from the left side. 
Fig. 3, skull of Diadectes phaseolinus, from above 
The letters signify as follows: m., medulla; ob. cerebellum ; opl., 
optic lobe; ep., epiphysis; ppe. , posterio r process of epiphysis; U/., 
lateral foramen; h., region of cerebral hemispheres ; v., cast of vesti- 
bule. 
PLATE XVII. 
Cranium of Belodon buceros Cope, from Southwestern New Mexico, 
from which the following cast was taken ; one-fourth natural size. Lat- 
eral, and one-half inferior and superior views. 
PLATE XVIII. 
Cast of brain-cases of Belodon buceros and Alligator mississippiensis, 
natural size. Figs. 1-3. Belodon buceros. Figs. 4-5. Alligator missis- 
sippiensis. Fig. 1. Right side. Fig. 2. Superior surface. Fig. 3. Right 
side. RE. Rhinencephalon. PE. Prosencephalon. ME. Mesenceph- 
alon. Ep. E. Epencephalon ae MO. Medulla oblongata. 
Ep. Epiphysis. Hyp. Hypophysis. ii. Optic nerve; v. Trigeminus; 
vi. Abducens; vii. Facialis; viii. EENE Op. Orbitopineal pro- 
cess or nerve, 
