326 ROY L. MOODIE 
in these forms. One very peculiar form is described in this new 
paper, Plagiosternum pulcherrimum, which has a remarkably 
frog-like skull. Another indication of the change to a land 
habitat is the nearly complete loss of the lateral line canals. 
The supraorbital canals are faintly indicated medially to the 
enormous orbits, but the other canals seem to have been lost. 
The pectoral girdle, so far as it is preserved, is of the aquatic 
type, typical of the large majority of the Labyrinthodontidae. 
It has been well known for some time that the lateral line 
canals have, among the fishes, a very definite effect upon the 
location of the various peripheral osseous elements of the cranium. 
Some of the bones are supposed to develop in response to a stimu- 
lus from the lateral line canals and are first formed as ossicles 
around and in response to the development of these canals. 
MeMurrich (’84, p. 279) observed this some years ago in the 
catfish, and in his discussion he states: 
In a young Amiurus, about 20 mm. in length, it was to be noticed 
- that wherever a mucous canal appeared in transverse section a ring 
of bone surrounded and protected it, so that each of these canals in the 
cranium was surrounded by an osseous tube. The bone was apparently 
deposited in membrane, and was evidently formed solely for the pro- 
tection of the mucous canal. In certain cases a bone, usually per- 
forated for the emission of a branch from the canal to a pore, became 
formed by a lateral extension of this osseous tube into the adjacent 
connective tissue. Instances of such bones are the infraorbital chain, 
the adnasals (lachrymals) and nasals. 
Similar observations have been made by Herrick (’01, p. 224): 
A detailed comparison of the lateral lines of Ameiurus and the sil- 
uroids described by Pollard * * * * *. brings out very clearly 
the peculiar and intimate relation existing between the canals and the 
dermal bones of the skull, a relation which has been recently emphasized 
by several writers. It is manifest that many of the bones, such as the 
extra-scapular and the suborbital series, have been developed for the 
canals. Conversely, it is equally evident that the canal is to a large 
extent dependent (probably as a cenogenetic adaptation) upon the 
bones and tends to disappear in their absence, as in the case of the infra- 
orbital line of Menidia. This relation between canals and bones is, 
however, not an inflexible one, as evidenced for example, by the fact 
