THE SCALES OF FRESHWATER FISHES. 373 



same sort of scales though lacking the characteristic lateral radii 

 of the Alestini and the Barbus. 



In some of the cyprinid alestiform scales the nuclear region 

 is broken up into polygonal areas, but in the curious African 

 Mormyridae 1 there is a characteristic system of anastomosing 

 radii, forming a network. This is unique, so far as material seen 

 by me shows, except for the case of Heterotis niloticus (Fig. 20), 

 a member of the ancient and now much reduced family Osteo- 

 glossidae. In this fish, which inhabits tropical Africa north of the 

 Equator, the network is extremely well developed. 2 



An extremely distinct and interesting type of scale is found in 

 the tench of Europe, Tinea vulgaris (Fig. 21). This seems to be 

 a relatively old type, formerly more abundant. Through the 

 kindness of Dr. A. S. Woodward, of the British Museum, I 

 was able to examine the miocene fossil species Tinea furcata of 

 Agassiz, and the nominal but apparently synonymous T. magna 

 of Winkler, and found the scales to be wholly characteristic of 

 the genus. It is a singular thing that in North America there 

 exists a fish called Algansea tincella, named tincella by Valen- 

 ciennes because of its resemblance to a tench, which has scales 

 of the same general type though not so extreme. Mr. Regan 

 has described two other species of the genus Algansea, A. affinis 

 and A. stigmatura, and he informs me that they have scales like 

 those of tincella. 



On the other hand, there are scales which so far as shape goes 

 resemble those of Tinea, and yet offer marked differences in the 

 details of the sculpture. Such is the scale of the Asiatic Schizo- 

 thorax biddulphii of Gunther (Fig. 22). Among the American 

 cyprinids, especially the smaller forms commonly known as 

 minnows, there are many scales which at first sight look alike. 

 In some cases, there is actually no definable difference, but often 

 sufficient familiarity with the scales enables one to recognize 

 them without difficulty. I illustrate a series of such forms, 

 Lavinia exilicauda (Fig. 23), Phenacobius mirabilis (Fig. 24), 

 Notropis galacturus (Fig. 25) and Pimephales anuli (Fig. 26) ; 

 also a similar European scale, Gobio fluviatilis (Fig. 27). In all 



Smiths. Misc. Coll., Vol. 56, No. 3, p. 2, figs, i, 2. 



2 Since this was written I have determined that all the Osteoglossidae, and also 

 all living Dipnoans (lung-fishes) have the radial network. 



