386 EDWARD PHELPS ALLIS, JR. 
A third type is found in the Holostei, and probably also in 
certain of the physostomous Teleostei, a premaxillary being 
present, and the maxillary having dental and dermal com- 
ponents. The dental component of the maxillary is formed by 
the fusion of the basal plates of teeth developed in relation to 
tissues that represent the anterior upper labial, the dermal 
component being a bone similar in origin to the dermal plates 
on the cheek of the fish. 
A fourth type is found in Polyodon. Here there is no pre- 
maxillary, and the maxillary resembles that of the Holostei, but, 
because of the absence of a premaxillary, it has been prolonged 
anteriorly until it meets its fellow of the opposite side in the 
median line. | . 
A fifth type is found in most of the Teleostei; the dental com- 
ponent of the holostean maxillary here becoming part of the. 
premaxillary, and forming a posterior prolongation of that bone 
which lies ventral and parallel to the maxillary and excludes it 
more or less from the upper margin of the mouth, while the 
dermal component of the holostean maxillary becomes the 
teleostean maxillary. 
In Amia and most of the Teleostei, an anterior portion of the 
primary upper lip persists as the maxillary breathing-valve. 
In Polypterus, Polyodon and Conger this breathing-valve is 
not found, the fold of the secondary upper lip apparently not 
here passing sufficiently anterior to the primary one to permit 
of the retention of the latter as an independent structure. In the 
Mammalia the primary upper lip (maxillary breathing-valve) 
becomes the secondary palate. 
The so-called vomers of Polypterus are mesial dermopalatines, 
lie morphologically in the floor of the suprapalatine recess, and 
do not contain the homologue of: the basal plate of the unpaired 
vomer of the Teleostei, which plate lies, morphologically, in the 
roof of that recess. The teeth on the two bones may, however, 
be homologous. 
Palais de Carnolés, Menton 
June 29, 1918 
