FISHES 3 53 





Photograph from Am. Mus. Natural History 

 FIG. 135. Common herring (Clupea). 



radii. In the herring group, some species have 

 cycloid scales, others ctenoid scales ; but when 

 the scales are ctenoid, they are still very differ- 

 ent from those of the fishes higher in the series. 

 A remarkable feature of many of the herring 

 family is the transverse circuli and radii of the 

 scales, running across from side to side. These 

 features may be seen very well in the scale of 

 the common herring. This peculiar structure 

 is evidently extremely ancient, as a scale from 

 the Chico Cretaceous of California, belonging 

 to a period fully five million years ago, is just 

 like that of a herring of the genus Pomolobus. 

 (b} Apodes (literally "without feet," meaning with- Eels 

 out ventral or pelvic fins). The eels and their 

 relatives, slender and mostly cylindrical fishes, 

 are found in fresh waters and in the sea. Scales 

 are present in some forms, absent in others, 

 but when present are minute and of peculiar 

 structure. The very young eel is a translucent, 

 band-shaped creature, so different from the 

 adult that naturalists formerly gave it a sepa- 

 rate name. The common fresh-water eel mi- 

 grates to the sea in winter, and there lays its 



