ORDERS OF FISHES. 



247 



The Skates and Rays {Batides) have the branchial openings placed 

 on the under side of the head, while the body is generally flattened 

 out into a. rhomboidal disc, the greater part of which is made up 

 of the enormously developed pectoral fins (fig. 177). In the Skates, 

 as in the Dog-fishes, the eggs are enclosed in leathery capsules, 

 familiarly known as "Mermaid's Purses." 



In another section of the Elasmobranchs, typified by the Chimcera 

 (fig. 176, B), though the internal structure of the gills is the same as 

 in the ordinary examples of the order, there is only a single external 

 gill-aperture. The group is therefore spoken of by the name of 

 Holocephali. 



Order VI. Dipnoi. 



The best-known, and until lately the only, forms included in this 

 order, are the very singular Mud-fishes {Lepidosiren), which are of 

 great interest from the many points of aifinity which they exhibit 



Fig. 17S.— A, Lepidosiren paradnxa, one of tlie Mud-fishes ; B, Front of the mouth of 

 the same, showing the teeth ; C, One of the overlapping scales, enlarged. 



to the Amphibia. The body of the Lepidosiren (fig. 178) is com- 

 pletely fish-like, and is protected by a covering of small, horny, 

 overlapping scales, which have the cycloid characters. There are 



