THE SCALES OF FRESHWATER FISHES. 371 



ingly represented in eastern Asia. From this circumstance one 

 might look for the earliest types of Cyprinidae also in America, 

 but the strong indications are that they are old-world forms, 

 the modern American cyprinids, with a few possible exceptions, 

 having arrived in comparatively recent times from Asia. Never- 

 theless, the carp family in this country must be only of compara- 

 tively, not actually, recent origin, since it has had time to de- 

 velop innumerable species, and a considerable series of endemic 

 genera. The distinctness of the American Cyprinid fauna 

 has indeed been emphasized by the scale work, it being shown 

 that the so-called Leuciscus, Rutilus, etc., of America are not con- 

 generic with the European fishes bearing these names. It is 

 probable, in fact, that all of the American Cyprinidse are gen- 

 erically distinct from those of Asia and Europe. 



Returning again to the bluefin scale, we can take a new point of 

 departure in Fig. 6, the Asiatic cyprinid Squaliobarbus curriculus. 

 Here the general form remains the same, except for a moderate 

 elongation, the apical circuli become more widely spaced, the 

 apical radii are evident, but there are no basal radii. A European 

 scale of nearly the same type is that of Leuciscus illyricus (Fig. 7). 

 In other cases, the scale may be more parallel-sided, with a broad 

 truncate base, as is shown in the Asiatic Labeo sladoni (Fig. 8) 

 and Rhinogobio typus (Fig. 9). 



In order to illustrate the value of scale characters within a 

 limited group, I give a series of figures of species usually referred 

 to Leuciscus, the dace and its allies. Leuciscus rutilus (Fig. 10) 

 and L. friesii (Fig. n) are European; L. hakuensis (Fig. 12) and 

 L. jouyi (Fig. 13) are Japanese. The remaining four are North 

 American, and because of their very different scales, and other 

 reasons, I have removed them to another genus, Richardsonius 

 Girard. R. orcutti from California (Fig. 14) constitutes a distinct 

 subgenus, the scale having basal radii. R. pulchellus (Fig. 15) 

 is of the Rocky Mountains. R. carletoni (Fig. 16) is a distinct 

 type from Maine, while R. thermopliilus (Fig. 17) inhabits warm 

 springs in Oregon. It will be observed that in the European 

 forms the large scales have exceedingly fine circuli. In the 

 American, the scales are very much smaller, and the circuli 

 are very coarse and widely-spaced. This is in general a charac- 



