MAXILLARY AND VOMER BONES OF POLYPTERUS 353 
a deep furrow that lies along the lateral edge of the posterior 
portion of the palatoquadrate, and which may be called, for 
reasons that will later appear, the dorsolateral diverticulum of 
the buccal cavity. In the other Selachii that I have examined 
this diverticulum was not so pronounced and evident as in 
Acanthias. 
Internal to the primary teeth of Acanthias, there is, as in 
Mustelus (Allis, 714, p. 355), a relatively large groove, from 
the bottom of which a thick fold of tissue arises and projects 
posteroventrally. I formerly considered this entire groove of 
Mustelus to represent the suprapalatine recess of my earlier 
descriptions of Chlamydoselachus, but a reexamination of my 
material shows that it is the furrow that lies postero-dorsal to the 
fold that alone represents that recess, and this furrow is in Acan- 
thias, as in Mustelus, simply a postpalatine groove and not a 
suprapalatine recess. Which of these two conditions is the more 
primitive, I am unable to determine, but the fold of Acanthias, 
which may be called the palatine fold, is certainly the homologue 
of the mucous fold that forms the posterior portion of the palatine 
shelf of my descriptions of Chlamydoselachus. This fold is 
found in all of the several species of the Selachii that I have 
examined, but it varies greatly in different species. In Scyllium 
it is a simple flap which strikingly resembles the maxillary breath- 
ing-valve of the Teleostei, but is related to the primary dental 
arcade instead of to the seconary one. In Lamna and Triakis 
it is as in Mustelus and Acanthias. In Centrina it is, as in 
Scyllium, a simple flap, but it projects externoventrally instead 
of posteriorly, and there is no furrow along its posteromesial 
edge. ~ | 
AMIA 
In this fish the conditions were examined in specimens varying 
from 10 mm. to 45 mm. in length. 
The supralabial furrow first appears as a pit-like depression 
that lies dorsal to the angle of the gape and immediately ventral 
to the suborbital laterosensory line, as shown in my figure of 
a 10-mm. specimen of this fish (Allis, ’89, fig. 4, pl. 31). In 
