VI EXTERNAL CHARACTERS 153 
erotesque appearance of the head of the Angler-Fish (Lophius) ; 
the huge high trunk and abbreviated tail of the Sun-Fish 
(Orthagoriscus); and the short high trunk and long tail of 
Notopterus (Fig. 354). 
In its external appearance the head perhaps differs more in 
different Fishes than any other part of the body. Long and 
flattened in the Skates and Rays, the head becomes short and 
high in most Holocephali and in many Teleosts, or is shaped lke 
a blunt cone, as in such Dipnoi as Protopterus and Lepidosiren ; 
or becomes long and pointed, as in the North American “ Gar 
Pike” (Lepidosteus); or, finally, as in the Hammer-head Shark 
(Sphyrna), the head may be produced into great lateral exten- 
sions, carrying the eyes at their extremities (Fig. 256, B). Apart 
from its relative shape and size, the appearance of the head may be 
further modified by the thinness of the investing scaleless skin, 
which readily allows the surface and contour lines of the bones 
of the skull to be seen through it, as in the Crossopteryeii, and 
in such Teleosts as the Siluroid genera Clarias and Callichthys ; 
or the skin, even if devoid of scales, may be so thick that scarcely 
any of the bones are visible externally. The exoskeleton, whether 
in the form of scales or bony plates, may extend to a varying 
degree on to the surface of the head in different Teleosts, or may 
even invest nearly the whole of the head. When, as is not infre- 
quently the case (e.g. many Scorpaenidae) certain of the bones of 
the skull are produced into projecting spines, the head assumes a 
singularly formidable appearance (Fig. 424). 
The mouth differs greatly in size and position. In existing 
Elasmobranchs it is generally crescentic in shape and always 
ventral in position, but in certain primitive fossil members of the 
group, as in the Palaeozoic Cladoselache, it is anterior and terminal. 
The Sturgeon and other living Chondroste1 have the mouth 
ventral. In the Dipnoi also the mouth is ventral, but is near the 
extremity of the snout. As a rule, the mouth is terminal or 
nearly so in the living Crossopterygii and Holostei, and in the 
great majority of Teleosts, although in the latter group it is 
occasionally distinctly ventral, especially when a snout is de- 
veloped, and it may sometimes look upwards by reason of the 
projection of the lower jaw in front of the upper. A pronounced 
“Deak ” is sometimes formed by the forward prolongation of both 
jaws, as in the Gar Pike (Lepidosteus), with the result that the 
