298 COPE. [Vo.. II. 
terminating at the narrow truncate extremity of the two bones. 
At the base of the opisthotic, and between it and the parasphe- 
noid, is situated the fenestra ovale. This is closed by the 
extremity of a columella auris, whose proximal part at least may 
be homologized with the stapes, since no other element corre- 
sponding with the latter is visible. The columella is then 
directed outwards, backwards, and upwards to the notch which 
is formed between the adjacent borders of the intercalars and 
suspensorium, where it terminates without having displayed any 
segmentation. This notch, which is present in all the Permian 
Batrachia known to me except Acheloma, may have been occu- 
pied by a membranum tympani, and that the Ganocephala had, 
like the Salientia, distinct external organs of hearing, thus dif- 
fering from the Proteida and Urodela. 
RHACHITOMI. 
The only genus in which I have observed ossicula auditus is 
Zatrachys (Cope). Here the parts resemble nearly those de- 
scribed in Trimerorhachis. The columella! is curved outwards 
and backwards, and terminates at the notch external to the os 
entercalare, which was, I suspect, covered by a membranum tym- 
pani as in the Salientia. 
PROTEIDA. 
In Necturus (Pl. XXIL, Fig. 1) the stapes is osseous and has its 
columella directed abruptly forwards. ‘It articulates with a cor- 
responding process of the squamosal bone, which extends pos- 
teriorly to meet it from the posterior bone of the latter. The 
quadrate part of the suspensorium of the mandible is exten- 
sively osseous. The distal extremity of the ceratohyal is not 
articulated with anything, but is connected with the quadrate 
by the hyosuspensorial ligament, and with the angle of the 
mandible by the mandibulo-hyoid ligament, as has been pointed 
out by Huxley.? 
In Proteus the relation of the stapes to the squamosal is 
similar in general to that in Necturus, but the connection 
1 Transactions American Philosophical Society, 1886, p. 290. 
2 Proceedings Zotlogical Society, London, 1874, p. 192, Pl. XXIX. Professor 
Huxley does not describe or figure the relation of the stapes to the squamosal bone. 
