2 CALIFORNIA FISH AND GAME. 



of the sharks, fossils of which are known back almost to the first of the 

 animals with a backbone. 



Though the typical sharks and the typical skates do not look at all 

 alike, we have sharks that do look very much like the skates, such as 

 the angel-shark; and skates, on the other hand, that are rather shark- 

 like. The character that may be most readily used to separate them is 

 the position of the gill slits. In the sharks the gill slits are on the side 

 of the body ; sometimes extending down on the lower surface, but the 

 upper end is always on the side. The skates and rays have the gill slits 

 altogether on the lower surface of the body. There are several other 

 characters that separate the sharks from the skates and rays, but they 

 are internal and need not be considered here. 



The skates and rays are specialized for life on the sea bottom. They are 

 not swift swimming fishes like the sharks that feed on other fishes, but 

 they depend on crabs and clams and such forms of animal life for their 

 food. The body by the development of the pectoral fins, which extend 

 forward along the side of the head, is flattened and disk-like. The 

 caudal fin may, or may not, be present. When it is not the tail is more 

 or less whip-like. None of them have an anal fin, and in many the 

 dorsals are also absent. When present the dorsals are far back on the 



Isuropsis glaiica. 



body or tail. The teeth may be in the form of a pavement, sometimes 

 being perfectly flat for crushing, or they may be with fine points. The 

 spiracle, which in the sharks is a small pore behind the eye, or else is 

 entirely absent, is in the skates and rays a large opening through which 

 water is introduced to the gills for breathing purposes. This avoids the 

 introduction of sand or sediment into the gill chamber as would prob- 

 ably happen did they take water through the mouth (as the shairks do) 

 when they lie flat on the sea bottom. 



The skates like the sharks have claspers in the male. These in the 

 young extend scarcely past the ventral fins, but in the adult they 

 develop to a large size (see figs. 5, young, and 10 and 11, adult) . 



I have changed the form of this paper from that on the sharks by 

 giving first a description of the different families of the skates and rays. 

 This saves repeating all of the characters under each species. Hence 

 in identifying any fish of this group it will be necessary to first find 

 its familv. 



