268 CHARACTERS OF VERTEBRATE ANIMALS 



scales), united firmly by their edges and having a very regular 

 arrangement in oblique rows, while the head is covered by paired 

 bony plates. 



The Reed-Fish is what a small Bichir might be imagined to 

 become if it were pulled out into an eel-like form and lost its 

 pelvic fins. 



Both these forms are distinguished as "Fringe-finned" Ganoids 

 on account of the structure of the paired fins ; while the remaining 

 recent Ganoids are " Ray-finned ", i.e. the paired fins have lost 

 the thickened basal portion and consist of a fan-like expansion 

 strengthened by the numerous diverging fin-rays, which may be 

 compared to the sticks of the fan. These ray-finned forms include 

 the Gar- Pikes, Sturgeons, and Bow- Fins of the present day. 



The Gar- Pike (Lepidosteus) is common in the fresh waters 

 of North America, and may be as much as 6 feet long. Covered 

 with firm armour like the Bichir, it differs not only in the structure 

 of the paired fins, but also in the presence of a single dorsal only, 

 while the head is drawn out into long but powerful jaws. 



Sturgeons are large fishes which have lost more or less of the 

 dermal armour, have a much elongated snout, and an unsym- 

 metrical tail like that of the Dog- Fish (see p. 258). The mouth 

 is on the under side of the body, at the base of the snout. The 

 Common Sturgeon (Acipenser) includes some twenty species, of 

 which the largest, a Russian form, is as much as 30 feet in length. 

 It is distinguished by its broad pointed snout, on the under side 

 of which are four sensitive thread-like structures (barbels), and the 

 presence of rows of broad keeled plates in the skin. Sturgeons 

 of this kind are widely distributed through the fresh waters and 

 along the coasts of the Northern Hemisphere. One species 

 (Acipenser sturio] is British, and may occasionally be se<tn in 

 fishmongers' shops. 



The Shovel -nose Sturgeon (Scaphirhynchus], native to the 

 Mississippi and the rivers of Central Asia, is of more elongated 

 form than the common form, and its dermal armour is more 

 complete, especially in the hinder part of the body. 



The two remaining kinds of Sturgeon both have teeth, while 

 the sorts so far mentioned are toothless; and they are further 

 distinguished by enormous snouts and the complete, or almost 

 complete, absence of armour. One, the Slender-beaked Sturgeon 

 (Psephurus) of the Yang-tse-Kiang and Hoang-ho rivers has a 



