368 T. D. A. COCKERELL. 



portant, have only emphasized his doctrine that the scale is of 

 great taxonomic value. I have paid little attention to the ganoids 

 and their relatives, and will not attempt to discuss them, here, 

 but may call attention to the important memoir by Goodrich 1 

 in which it is shown that the so-called ganoid scales can be divided 

 into three very distinct groups, called the cosmoid, palaeoniscoid 

 ganoid and lepidosteoid ganoid. Mr. Goodrich, having distinctly 

 differentiated these types, applies his work to the classification 

 of some difficult forms, with striking results. 



Teleostean scales, the ordinary imbricated readily removable 

 scales of fishes, were classified by Agassiz as cycloid and ctenoid, 

 and his names are still in current use. The cycloid scale is one 

 in which the apical margin is what a botanist would call entire, 

 that is without teeth or serrations. The ctenoid or comb-like 

 scale has the margin dentate, serrate or spiny. It is now w r ell- 

 known that these are not fundamental divisions, some families 

 having both ctenoid and cycloid types, and as Shaler has stated, 

 it is possible for both kinds to exist on a single flat-fish. Never- 

 theless, the distinction is usually an important one, while the 

 scales have innumerable other characters of value, not used in 

 Agassiz's sytem of classification. 



My own work with fish-scales had what might be called an 

 accidental beginning. In the course of class-work, my students 

 and I took occasion to examine the scales of the fresh-water 

 fishes of Colorado. We soon perceived that they had excellent 

 distinctive characters, and thereupon sought literature on the 

 subject. Failing to find anything satisfactory, we wrote to Dr. 

 D. S. Jordan, who promptly gave us the desired information, 

 or rather, indicated the lack of it. Girard, in his report on the 

 fishes of the Mexican Boundary Survey, had given numerous 

 figures of the scales of fresh-water fishes, but had not discussed 

 or classified them. About fifty years ago it appears that it was 

 seriously intended to work up the lepidology of the American 

 teleosts, but for some reason nothing came of it, beyond the 

 publication of \he figures mentioned. Later, Dr. Boulenger gave 

 me access to the work of Fatio (1882), in which the scales of all 

 the fishes of Switzerland are figured; also to the great work of 



l Proc. Zool. Soc. London, 1907, pp. 751-774. 



