359 
surface of the horizontal palatine shelf, a mucous fold with a support- 
ing core of cartilage thus being formed, dorsal to which there is a large 
and deep suprapalatine recess in the roof of the mouth cavity. When 
the mouth is opened and shut some slight movement must necessarily 
be given to this mucous fold, and the overlying recess must be corre- 
spondingly enlarged or diminished in capacity. 
The cartilaginous lateral wall of the suprapalatine recess is per- 
forated, on either side, by the nasal fontanelle, as can be seen by ref- 
erence to Goopry’s figure, this fontanelle being, in its relations to 
the bounding cartilages, the apparently strict topographical homo- 
logue of the fenestra choanalis of amphibians (Auuıs, 1913). The 
nasal cavity of Chlamydoselachus is thus separated from the supra- 
palatine recess by membranous and mucous tissues only, and if these 
tissues were to be secondarily perforated, as strictly similar tissues 
are said to be so perforated in the higher mammals, an internal nasal 
aperture would be formed which would lie directly above the hori- 
zontal palatine shelf. If a median longitudinal keel, such as is found 
in many selachians (GEGENBAUR), were then to be developed along 
the ventral surface of this portion of the neurocranium, a condition 
would arise which would strikingly suggest, if it does not actually 
foretell, the secondary palate of mammals. 
Wishing to know if this palatine shelf and suprapalatine recess 
were peculiar to Chlamydoselachus among the Chondropterygii, I have 
examined several somewhat dilapidated specimens that I have of 
Heptanchus, Cestracion, Mustelus, Carcharias, Torpedo and Chi- 
maera. In Mustelus, the best preserved of the several specimens 
examined, there is a long and relatively large groove that lies inme- 
diately dorso-posterior to the palato-quadrate, but along the internal 
instead of the external surface of the cartilage, the transverse axis 
of the palatine process of this fish being direeted dorsally or dorso- 
anteriorly instead of postero-mesially as it is in Chlamydoselachus. 
This difference in the position of the axis of this cartilage totally 
changes the conditions in the two fishes, as does also the difference 
in the position of the mouth, practically terminal in Chlamydose- 
lachus and decidedly postero-ventral in Mustelus; but, nevertheless, 
the groove in the one would seem to correspond to the pocket in the 
other. The median portion of the groove, in Mustelus, lies in the depres- 
sion shown immediately posterior to the process V of GEGENBAUR’S 
figures of this fish, and from there the groove extends posteriorly across 
23* ’ 
