No. 2.] LATERAL LINE IN EXTINCT AMPHIBIA. 527 
x 
edges of the grooves more or less perpendicular, but in 
Metoposaurus the canals are deep and the borders are sharply 
incised. 
Why the lateral line canals are more deeply incised on the 
skulls of the Stereospondylia is not easy to determine. This 
suborder is the most highly specialized of all of the Stego- 
cephala and it is a part of this specialization that the canals 
are deeply incised. The canals become more strongly marked 
as the individual grows older, and it is possible that the same 
will hold for the suborder. This suborder began, or at least 
we find the first evidences of it, in the Carboniferous at the 
same time that all of the other groups are represented by 
well-developed forms. All of the other groups, however, died 
out or became modified into other forms, so far as our pres- 
ent knowledge goes, before the Triassic or at least we know 
nothing of them after the close of the Permian. The Ste- 
reospondylia, however, did not become extinct until the latter 
part of the Trias or the early Jurassic. It is thus the long- 
est lived of any of the groups of the Stegocephala as such, 
and for this reason we may consider that the lateral line canals 
are strongly developed. In Eryops, attention has already been 
called to the coarse pits occurring in the bottonis of the canals, 
and it must be stated that the canals in Eryops are not so 
well-developed as in the labyrinthodonts. It is thus evident, 
if we take Eryops to be a primitive form, that the primitive 
characters of the lateral line canals are the occurrence of deep 
coarse pits in the bottoms and their broad character and weak- 
ness of development. In other words the lateral line canals 
in the Stegocephala are, in their earliest development, rows 
of pits which later become developed into well-defined grooves. 
Whether the condition described for Eryops will hold for other 
of the Temnospondylia remains to be determined. In the 
Stereospondylia the canals, as stated, are usually clearly 
marked and often have smooth bottoms. 
In the collection of the University of Chicago, there are two 
perfect skulls of labyrinthodonts, collected some years ago by 
Mr. N. H. Brown, of Lander, Wyoming, in the Triassic rocks 
