No. 2.] LATERAL LINE IN EXTINCT AMPHIBIA. 513 
or of specialization, for I have observed that in the more 
generalized forms the line canals are roughened by the vascular 
pits, but in the highly specialized labyrinthodonts the bottoms 
of the canals are usually rather smooth, and this smoothness 
increases as the animal grows older. The canals of the 
lateral line organs are always open and never have the canals 
roofed over as is the case, according to Dean (4), in some of 
the Arthrognathid fish-like vertebrates. 
Pollard (5), Baur (6), and Allis (7) have attempted some 
correlation of the cranial elements of the fishes and Stego- 
cephala on the basis of the lateral line system. Baur’s work 
had to deal with the stegocephalan side of the question and 
the others treated the question from the fish point of view. 
Allis’ paper on the homologies of the squamosal and other ele- 
ments is especially instructive. Pollard, according to Baur, 
did not fully understand the arrangement of the lateral line 
organs in the Polypterus which he was studying, having 
failed to comprehend the significance of the occipital cross- 
commissure. Baur did not complete the homologies of the 
crania of the fishes and stegocephalans, but carried the cor- 
relations as far as was then possible. In my studies on the 
Carboniferous Amphibia, I have been led to investigate the 
conditions of the lateral line system in the extinct forms to 
see if some definite idea might be formed as to the homology 
of the squamosal and supratemporal elements in the skull 
of the Stegocephala. The investigation was undertaken in 
the hopes of ascertaining just what the element which lies 
laterad to the parietal in most forms of the Stegocephala is, 
whether it is the squamosal, prosquamosal or supratemporal, 
all of which names have been applied to it by various authors. 
An attempt has been made to correlate the lateral line canals 
in the Stegocephala with those of the fishes and recent 
Amphibia. In the accompanying diagram (Fig. 1), there 
are represented all of the canals which occur on the crania of 
the Stegocephala. They do not all occur in any one species 
nor indeed in any one group, but are all found in more or less 
well-developed form in some of the extinct Amphibia. The 
