MORPHOLOGICAL REVISION I43 



There are four pairs of branchial hones in one specimen described by 

 Williston (69). "The outer pair, lying close to the inner margin of the man- 

 dibles, have the posterior end thickened and recurved, hook-like, to abut 

 against or approach the hind side of the quadrate. I would take them to 

 be ceratobranchials, save for the fact that a pair of nearly square bones very 

 clearly articulate with the anterior ends, which must be ceratobranchials. 

 To the inner side and progressively more posterior, lying symmetrically, 

 are three pairs of epibranchials, the inner and hindmost represented in 

 the specimen only by their anterior ends, the posterior portion being 

 broken off with the atlas. The two outer pairs, at least, are thickened 

 and truncate at each end, and are partly hollowed or cancellated, like all 

 other bones of the skeleton. The first of these pairs also seems to have a 

 thickened and recurved posterior extremity." 



The vertebral column: Just over the occipital condyle are two small 

 plates, which probably represent a proatlas. There is no distinct atlas or 

 axis, and the vertebrae of the column are all similar. The centrum is per- 

 forate, and the cavity is widely open, so that the notochord was very little 

 constricted. The sides are marked by deep pits, which divide the lower 

 surface of the centrum into three ridges, hence the name of the species. 

 The neural arch is free from the centrum and the two halves are separate. 

 The zygapophyses are nearly horizontal. There is no trace of intercentra. 



The ribs are single-headed, rather long, and proportionately stout. 

 They are frequently broken at the proximal end and present the appear- 

 ance of having been anchylosed to the centrum and broken off. 



Williston reported finding small limb bones among the specimens of 

 Lysorophus, but it is very uncertain whether these belong to Lysorophus; 

 at least four genera have been found in the same beds, Gymnarthrus, Cardio- 

 cephalus, young Diplocaulus, Lysorophus. Thousands of series of Lysorophus 

 vertebrae have been found with very perfectly preserved ribs and centra, but 

 without any trace of limbs associated. It seems, with all of the suggestions 

 of a snake-like body, that it is less likely that these limb bones belonged 

 with Lysorophus than with some of the other forms. 



The position of Lysorophus is not certain. That it is an amphibian 

 seems well established. Broili's interpretation of the condyle as single is 

 certainly not borne out by numerous other specimens. The same may be 

 said for the basicranial region; it is certain that the broad fiat plate can 

 not be reckoned as a basioccipital element; parts taken for this in several 

 specimens have proven to be fragments of the proatlas or first vertebra. 

 In addition, Williston cites the tricarinate vertebrae, the sutural division 

 of the neural arch, and the neuro-central attachment of the ribs as distinctly 

 amphibian. 



It is not so apparent that the Lysorophus was a Urodele of the group 

 Ichthyoidea, as declared by Williston. The apparently limbless condition 

 and the probable position of the eyes far forward in the orbital spaces 

 suggest some affinity with the limbless amphibians. The singular fact 

 that the specimens are always found in a more or less tightly rolled up 

 condition, led the late Dr. Baur to suggest that these were embryonic forms, 

 but the enormous numbers and well-ossified condition negative the idea. 

 It is more probable that they were, as Williston suggests, naked-skinned, 

 mud-burrowing creatures, that met their death by suffocation in large, 

 shallow pools, which were in process of gradual desiccation. This would 



