PISCES 133 



out teeth in the adult. The scales are remarkable in that they are ar- 

 ranged in five widely separated longitudinal rows of keeled bony ele- 

 ments. The dermal bones of the roof of the skull are fused into a solid 

 shield. The sturgeons inhabit the inland lakes and seas, being found 

 in our own Great Lakes, in the Black Sea, the Caspian Sea, and the 

 tributaries of these lakes and seas. They feed upon moUusks, worms, 

 small fishes, and vegetation, the mouth being protruded as a cylin- 

 drical spout and thrust into the mud in search of food. They some- 

 times reach a very large size — ^individuals having been taken that 

 weighed 2,760 and 3,200 pounds. The Russian delicacy, caviar, is 

 made of the eggs of sturgeons. The flesh of the sturgeon is also an 

 excellent food and is largely used. 



Many extinct Chondrostei are known, and in every case they are 

 nearer the type exempUfied by the Crossopterygii than they are like 

 the modern Spoon-Bill and sturgeon. It is therefore highly probable 

 that the group was derived from the Crossopterygii. 



Order III. Holostei 



This rather large and varied assemblage of fishes is, with the 

 exception of two genera, extinct. It is probably from this order that 

 the malacopterygian Teleostei arose, since there is a gradual transi- 

 tion between the two groups. As the name indicates, these fishes have 

 a completely ossified skeleton, much like that of the Teleostei. The 

 scales are either rhombic or cycloid but are covered externally with 

 a hard coating of ganoin. If one begins with the oldest fossil Holos- 

 tei and proceeds through a series up to more recent forms, it is pos- 

 sible to trace the development of many of the features that charac- 

 terize the present teleosts and to note the elimination of many of 

 the more primitive teleostome characters. The Holostei are repre- 

 sented to-day by two families, the Lepidosteidoe (Gar-pikes) and the 

 AmiidiB) Bow-fins. Only two species of Gar-pike and one species of 

 Bow-fin {Amia calva) exist to-day. 



The Gar-pikes, Lepidosteus (Fig. 72, A), are fresh-water fishes 

 of the United States and Canadian waters. They are elongated crea- 

 tures with long slender snouts heavily armed with teeth. They are 

 predaceous and kill great numbers of other fishes. In some regions a 

 bounty is placed on their heads. The great Alligator Gar reaches a 

 length of ten feet or more and with its huge jaws is a really formidable 



