Cope.] ^^^ [April 15, 



pared with the contraction of the part behind the epiphysis. The hypoph- 

 ysis is distinct but not large, and occupies a fossa of the base of the 

 cranial cavity, very much shorter than that possessed by the Alligator 

 viississippiensis. The optic nerves issue immediately above and anterior 

 to it. 



Comparison with the brain of Diadectes. In these Proceedings for 1885, 

 p. 234, I have described a cast of the brain- chamber of a species of the 

 Diadectidse from the Permian bed of Texas. As a successor of the Dia- 

 dectes, and as descendent of probably one of the Clepsydropidfe, consider- 

 able interest attaches to a comparison of the brain of Belodon with it. 



The first point which arrests the attention in making the comparison, is 

 the similarly huge size of the epiphysis in the two types. A foramen on 

 each side of the base of the epiphysis in the Diadectes gave exit to a pro- 

 cess similar to that which enters the orbitopineal canal in the Belodon, 

 and which I called the lateral process of the epiphysis in the latter. (Plate, 

 figs. 1-3, 1 0- The processes are probably homologous in the two genera, 

 but In the Diadectes they did not extend to the orbit, unless they were 

 continued in membranous walls. There is little resemblance between the 

 two brains in other respects, but they agree in the small size of the pros- 

 encephalon, and in the complete enclosure of the rhineucephalon by 

 osseous walls. In the Diadectes there is no optic foramen, but a huge 

 trigeminus ; in Belodon, an optic foramen, and a very small trigeminus. 



The presence of such a huge epiphysis in the Belodon as compared with 

 its very small size in modern crocodiles, is a point of much interest, and 

 points to its inheritance from the reptiles of the Permian. Bat if, as is 

 probable, it contained the pineal eye, the latter could not receive light 

 directly from above, since the parietal foramen is wanting. The presence 

 of a communication with the orbit becomes interesting in this connection. 

 A minute foramen passes from the base of the rhineucephalon into the 

 orbit in the alligator, but the homology with the canalis orbitopinealis 

 is by no means made out. The nervus orbitopinealis may have supplied 

 the lack of light due to the closure of the parietal foramen, but in what 

 way we are left to conjecture. 



The equality of size of the brain of the Belodon to that of the existing 

 alligator is a point of interest. 



There is some reason to suspect that the Diadectes relied exclusively on 

 the pineal eye for the sense of sight. The species of the family were 

 probably subterranean in their habits, since their humeri indicate great 

 fossorial power, resembling those of the existing monotremes, and even 

 the mole. The vertebra are locked together with the hyposphen beside 

 the usual articulations, and the arches of the neural canal form an 

 uninterrupted roof from the skull to the tail, of extraordinary thickness 

 and strength. That the species were not aquatic is rendered probable by 

 the fact that the orbits do not look upwards. Their superior borders are, 

 on the contrary, prominent and straight. Add to this fact the apparent 



