Cope.] 574 [March 7, 



The orbit occupies part of the anterior third of the length. It is bounded, 

 in front by an obtuse preorbital process, and posteriorly by a laterally 

 expanded and decurved postorbital process. The latter bears an articular 

 facet on its posterior and inferior face. The top of the muzzle is exca- 

 vated by a fontanelle which does not extend posterior to a line connecting 

 the preorbital processes. 



There is a prominent cup-shaped occipital condyle. On each side of 

 the cranium a short distance anterior to it, is a prominent process extend- 

 ing outwards and a little backwards, which is excavated on its inferior 

 side, but whose posterior side is decurved, so that the inferior concavity 

 looks partially forwards. Into this cavity, and abutting against the 

 decurved posterior edge, is a lateral process of the basal axial bone of the 

 skull, which I take to be homologous with the lateral alee which occupy 

 the same position in the sharks. Anterior to this junction no doubt the 

 hyomandibular bone was suspended, for I suspect that it was articulated to 

 a small condyle which is wedged into the fissure between the inferior and 

 superior elements described, a centimeter anterior to their posterior 

 extremities. This condyle is a distinct element of a subglobular form. 



The interorbital plane is continued posteriorly, bounded on each side by 

 a depression which probably corresponds to the temporal fossa of higher 

 vertebrates. The edges of this plane are thus well within the lateral 

 borders of the cranium. The plane rises a little posteriorly, and is split 

 into two narrow wedge-shaped processes, which project freely upwards 

 and backwards. The rather short remaining part of the roof of the skull 

 has a keel or sagittal crest on the middle line, which descends gradually 

 to the foramen magnum. 



The base of the skull forms a continuum from the edge of the large occi- 

 pital cotylus to the acuminate anterior extremity. The lateral basal alse 

 are subcylindric, and are separated from the basicranial axis by a fissure 

 for a short distance, and then unite with it. Two or three foramina ante- 

 rior to this reunion, are in line with the defining fissure just mentioned. 

 The basis cranii sends out a process on each side below the postorbital 

 processes, giving a cross-shape to this part of the base of the skull. An- 

 terior to this point it is free from other elements and contracts to an 

 acuminate apex. 



The cranium is segmented, but a clean specimen is necessary to per- 

 mit the straight sutures to be seen. In the first place, there is a distinct 

 occipital bone, which includes exoccipital and basioccipital elements com- 

 bined. The latter includes the large occipital cotylus, as in the Rhachi- 

 tomoiis batrachian Trimerorhachis, and differs from the structure seen in 

 the Lepidosirenidse, where exoccipital elements only are present. The 

 occipital extends but a short distance on the inferior face of the axis. It 

 is preceded directly, and without imbrication, by a continuous axial ele- 

 ment. If we recognize in the granular character of the tissue evidence 

 of true ossification of the chondrocranium, we have here true continuous 

 sphenoid and presphenoid bones. 



