SCALES. 47 



forms between the cycloid and ctenoid types. Both kinds of 



Fig. 12. — Ctenoid scale of Scato- 

 phagus multifasciatus (magn.) 



Pig. 13. — Ctenoid scale of Platy- 

 cephalus cirrhonasus (magn.) 



Fig. 14.— ^Ctenoid scale of Gobius 

 ommaturas (magn.) 



Fig. 15. — Ctenoid scale of 

 Lethrinus (magn.) 



scales may occur not only in species of the 

 same genus of fishes, but in the same iish. 



Oanoid scales are hard and bony, covered 

 with a layer of enamel ; they are generally 

 rhombic or quadrangular, rarely rounded and 

 imbricate; and arranged in oblique rows, 

 those of one row being linked together by 

 an articulary process. This type of scales, 

 common in fossil Ganoid fishes, occurs 

 among recent fishes in Zepidosteus and Polypterus only, 



Fig. 16. 

 Ganoid Scales. 



