LIPS AND NASAL APERTURES IN FISHES 169 
A supramandibular furrow occurs in normal position, external 
to an anterior process of the mandibular labial, shown in Vetter’s 
figures of this fish. The furrow is deep, its deeper portion ending 
posteriorly dorsal to the ventro-anterior end of the postlabial fur- 
row, while its larger, superficial portion is confluent with the corre- 
sponding portion of the latter furrow. The supramandibular 
fold differs from that in the Selachii in that its hind end has been 
pushed downward on to the external surface of the mandible, 
this being associated with a change in direction of the line of the 
angle of the gape, which, in the Plagiostomi, is directed from 
within antero-laterally. In Chimaera it is directed ventrally 
and but slightly laterally, the inner end of the line having been 
carried upward and forward, while its outer end has dropped 
dewnward upon the external surface of the mandible. The 
mandibular preangular labial crease starts from near the inner 
end of this line and, after running at first symphysially along the 
lateral edge of the primary lower lip, turns outward across the 
outer edge of the secondary lower lip to a point dorsal (oral) to 
the anterior end of the supramandibular furrow. There the 
anterior end of the crease and furrow are connected by a slight 
depression in the dermis. This crease thus cuts out of the 
secondary lower lip an important preangular portion which corre- 
sponds to the little islet cut out of this lip by the crease in 
Mustelus. The labial fold overlaps the larger part of this islet, 
the part so overlapped being thinner than the part beyond it 
and being separated from it by a low ledge. This ledge corre- 
sponds to the outer edge of the secondary lower lip of the Selachii, 
and forms the edge of the functional lip of Chimaera when the 
mouth is widely opened; but it is not the functional lower lip 
when the mouth is closed, the functional lip then being formed 
by the mesial edge of the preangular islet. In other words, the 
posterior portion of the secondary lower lip has been turned 
downward upon the outer surface of the mandible, and a broad 
and V-shaped portion of its inner surface is presented externally. 
The angle of the V is directed symphysially, and its mesial arm 
forms the functional lip when the mouth is closed and the lateral 
arm the functional lip when the mouth is opened. The former 
