The Holocephali, or Chimeras 219 
gium and without recognizable analogue of the three large 
cartilages seen in the sharks, the propterygium, mesopterygium, 
and metapterygium. In the mouth, instead of teeth, are de- 
veloped flat, bony plates called tritors or grinders, set endwise 
in the front of the jaws. The gills are fringe-like, free at the 
tips as in ordinary fishes, and there is a single external opening 
for them all as in true fishes, and they are covered with a flap 
of skin. These structures are, however, quite different from 
those of the true fishes and are doubtless independently de- 
veloped. There is no spiracle. The skin is smooth or rough. 
In the living forms and most of the extinct species there is a 
strong spine in the dorsal fin. The ventral fin in the male has 
complex, usually trifid, claspers, and an analogous organ, the 
cephalic holder, is developed on the front of the head, in the 
adult male. This is a bony hook with a brush of glistening 
enameled teeth at the end. The eggs are large, and laid in 
oblong or elliptical egg-cases, provided with silky filaments. 
The eggs are fertilized after they are extruded. Mucous chan- 
nels and lateral line are highly developed, being most complex 
about the head. The brain is essentially shark-like, the optic 
nerves form a chiasma, and the central hemispheres are large. 
The teeth of the Chimeras are thus described by Woodward, 
vol. 2, pp. 36, 37: 
“Tn all the known families of Chimeroids, the dentition 
consists of a few large plates of vascular dentine, of which 
certain areas (‘tritors’) are specially hardened by the depo- 
sition of calcareous salts within and around groups of medullary 
canals, which rise at right angles to the functional surface. In 
most cases there is a single pair of such plates in the lower jaw, 
meeting at the symphysis, while two pairs are arranged to 
oppose these above. As a whole, the dentition thus closely 
resembles that of the typical Dipnoi (as has often been pointed 
out); and the upper teeth may be provisionally named pala- 
tine and vomerine until further discoveries shall have revealed 
their precise homologies. The structures are sometimes de- 
scribed as ‘jaws,’ and regarded as dentaries, maxilla, and 
premaxille, but the presence of a permanent pulp under each 
tooth is conclusive proof of their bearing no relation to the 
familiar membrane-bones thus named in higher fishes.” 
