The Holocephali, or Chimeras 223 
ture resembles that seen in the deep-sea shark, Mitsukurina, 
and in Polyodon. In Rhinochimera pacifica of Japan the teeth 
in each jaw form but a single plate. In Harriotta raletghana, 
of the Gulf Stream, they are more nearly as in Chimera. Both 
are bathybial fishes, soft in texture, and found in great depths. 
The family of Callorhynchide, or Antarctic Chimeras, includes 
the bottle-nosed Chimera (Callorhynchus callorhynchus) of the 
Patagonian region. In this species the snout is also produced, 
a portion being turned backward below in front of the mouth, 
forming a sensory pad well supplied with nerves. 
Ostracophori.—In natural sequence the class or subclass of 
Ostracophores follows the sharks and Chimeras. 
As all the Ostracophort are now extinct, we may here pass 
them by without further discussion, referring the reader to the 
full treatment in the ‘‘Guide to the Study of Fishes.’”’ These 
are most extraordinary creatures, jawless, apparently limb- 
less, and enveloped in most cases anteriorly in a coat of mail. : 
In typical forms the head is very broad, bony, and horseshoe- 
shaped, attached to a slender body, often scaly, with small 
fins and ending in a heterocercal tail. What the mouth was 
like can only be guessed, but no trace of jaws has yet been 
found in connection with it. The most remarkable distinctive 
character is found in the absence of jaws and limbs in connec- 
tion with the bony armature. The latter is, however, sometimes 
obsolete. The back-bone, as usual in primitive fishes, is de- 
veloped as a persistent notochord imperfectly segmented. The 
entire absence of jaw structures, as well as the character of the 
armature, at once separates them widely from the mailed Arthro- 
dires of a later period. But it is by no means certain that 
these structures were not represented by soft cartilage, of which 
no traces have been preserved in the specimens known. 
