ORDE'.IS OF FISHES. 



247 



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

 on the imder 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 C/iimwra 

 (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 grou]i is therefore spoken of by the name of 

 Ifolocep/iali. 



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 aftinity which they exhibit 



Fig. I7S.— A, Lepidnnren paradnxa, one of the Murl-fislies ; B, Front of the mouth of 

 the same, showin^^ the teeth ; 0, One of tlie overlapphig .scales, eolarged. 



to the Ainphihia. The body of the Lepidosireii (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 



