646 ALLIS. AViOL. xT: 
tral edges of the second and third basibranchials to the ventral 
angle of the latter piece. The dorsal surface of the entire line 
has a fairly even width. 
In a 20 mm. specimen, examined in sagittal sections, the basal 
line consisted of three elements, as in the adult; in two 14 mm. 
specimens, examined in sagittal and horizontal sections, the 
arrangement was somewhat different. In both these latter 
specimens the second element was distinctly continuous with 
the posterior end of the first element, the two pieces being 
separated ventrally by a deep fissure, but connected dorsally by 
a thin bridge of cartilage, exactly as the portion called by van 
Wijhe the basihyal was connected with the anterior end of the 
element. This latter connection was as distinctly marked as in 
the adult. The third element seemed to be in process of separa- 
tion from the second, the outlines of the abutting ends of the 
two pieces being indicated and evident, but the space between 
them filled with semi-cartilaginous tissue. These early stages in 
Amia, and the continuous basal line in embryos of Lepidosteus 
and Acipenser (Parker), therefore indicate that the basal line 
is, In ganoids as it is in teleosts (No. 118), originally a 
continuous mass, which later separates into several members, 
rather than that it is formed by the fusion of several originally 
independent members, Amia representing an intermediate con- 
dition in the process, as van Wijhe’s statement that the basihyal 
is partly fused with the first basibranchial would seem to in- 
dicate (No. 120, p. 284). 
No indication of a separate basihyal was found in Amia, 
either in the adult or in larvae. 
b. Branchial Arches. 
The first and second branchial arches (Figs. 49-55, Pls. 
XXXIII-XX XV) consist each of a hypobranchial, a cerato- 
branchial, an epibranchial, and one or two pharyngobranchials ; 
the third and fourth each of a hypobranchial, a ceratobranchial, 
and an epibranchial, and a single large piece which serves as a 
pharyngobranchial for the two arches, but is considered by van 
Wijhe as the pharyngobranchial of the third arch only. The 
