THE SCALES OF FRESHWATER FISHES. 375 



Oregon. (2) Scale broad, large. Napa River (California). 

 (3) Scale oblong, more weakly sculptured. Ukiah Creek; 

 Russian River (California). (4) Scale oblong, strongly sculp- 

 tured. Conchilla Creek (California). 



It appears from this that there is a broad-scaled form to the 

 north coming south as far as Gualala River. From this it is only 

 a few miles to Russian River, w r here the fish is oblong-scaled. 

 Passing beyond, however, we find another broad-scaled variety 

 in Napa River. It is suggested that the broad-scaled fishes, 

 when in competition with the oblong-scaled, may get the better 

 of them, and that the Napa River fish represents an invasion from 

 the north away from the coast. All this, however, is at present 

 based on far too little evidence, and is given here partly as an 

 example of the kind of problem the scale-work brings up, and 

 partly in the hope that someone will make an exhaustive study 

 of the matter. Up to the present, I have not been able to get 

 any further information, beyond what is given by Dr. Snyder 

 in Bull. Bureau of Fisheries, XXVII, p. 175. In general, Dr. 

 Snyder's results, based on other than scale characters, agree with 

 mine, but he finds no difference between the fishes of Russian 

 and Napa Rivers. No less than five specific names have been 

 given to M. symmetricus as now understood; probably two or 

 three of these will be available for the necessary segregates. 

 While most fish scales fall readily into a systematic arrangement, 

 we occasionally meet with one which differs greatly from any 

 other known to us. Such is the scale of Kneria cameronensis 

 Boulenger (Fig. 31), a small fish belonging to a peculiar family 

 found only in tropical Africa. In this the radii run from one end 

 of the scale to the other and the circuli are for the most part 

 broken up into peculiar marks between them. 



The study of fish-scales opens up a vast new field, the scales 

 of most of the common fishes being still undescribed. Fish scales 

 also may claim our attention for their beauty as microscopical 

 objects. Their preparation involves no difficulty; they are 

 best mounted dry between thin microscopical slides; or when 

 small, they may be mounted on a slide under a cover glass. 

 At first, I placed them in balsam, but this greatly obscures the 

 markings, and is altogether undesirable. 



