180 EDWARD PHELPS ALLIS, JR. 
and in the Holocephali, from the coalescence of the lips of oppo- 
site sides of a naso-buceal groove. Greil (13) says that, in 
embryos, both apertures lie in the roof of the mouth, that they 
arise, as in the Teleostei, by the coalescence of the opposite 
edges of a nasal groove formed by the elongation of the primitive 
nasal pit, and that no naso-buccal groove is ever developed in 
this fish. 
Huxley (’76) described two cartilages in this fish which he 
considered ‘to be the homologues of the anterior and posterior 
upper labials of the Selachii, one of them lying between the 
anterior and posterior nasal apertures and the other posterior to 
the latter aperture. Bridge (98) later concluded that the 
anterior of these two cartilages was not a labial cartilage, but a 
persisting remnant of the ventral wall of the nasal capsule, and 
he called it the subnasal cartilage. The posterior cartilage he 
was inclined to consider, with Rose (’92), to be the homologue 
of the so-called antorbital process of Lepidosiren and Protop- 
terus, but he suggested that it might be the homologue of a 
wholly separate and independent cartilage, found, in the latter — 
fishes, which he considered to be unquestionably the homologue 
of one of the upper labial cartilages of the Selachii. Firbringer 
(04) accepted Bridge’s conclusion regarding the anterior of 
these two cartilages of Ceratodus. Regarding the posterior 
cartilage, he says that it is the homologue of the upper labial 
cartilage of Bridge’s descriptions of Lepidosiren and Protop- 
- terus, but that this cartilage is, in all these fishes, a detached 
portion of the chondrocranium and not the homologue of either 
of the upper labials of the Selachii. Because of this derivation, 
of the cartilage he calls it the postnasal cartilage, He describes 
and figures a cross-bar of cartilage lying lateral to the posterior 
nasal aperture and connecting the subnasal and postnasal carti- 
lages, and he says that it is a secondary, protective arrangement, 
developed in relation to these cartilages and the nasal apertures. 
Huxley neither describes nor shows this cross-bar of cartilage 
connecting his two upper labials. 
In a large but not well preserved head of this fish I find the 
cross-bar of cartilage described by Fiirbringer, but in my speci- 
