NOTE ON THE MICROSCOPIC STRUCTURE OF THE 

 SCALE OF AMIA CALVA. 



H. W. MACKINTOSH, B.A., 

 Senior Moderator in Natural Science, Trinity College, Dublin. 



[Read December 17th, 1877.] 



About four years ago Professor Macalister, Director of the Museum 

 of Comparative Anatomy and Zoology in the University of 

 Dublin, obtained a fine specimen of the North American Ganoid 

 Amia calva, and before sealing it up and placing it in the 

 Museum, kindly gave me one of the scales for microscopic ex- 

 amination. Pressure of other matters prevented me at the time 

 from bestowing upon it more than a cursory glance, and it has 

 lain mounted in my cabinet almost forgotten till a few months 

 ago, when, having occasion to demonstrate some points in the 

 structure of the scales of fishes, I was led to give it a more careful 

 study, which brought to my notice a peculiar form of lacunae 

 which does not seem to have been hitherto described, and which 

 may be of interest to the members of this Society. 



Amia is commonly described as a ganoid with overlapping 

 cycloid scales. I submit that in the face of figs. 1 and 2, 

 the term cycloid must be abandoned and replaced by ctenoid. 

 The mistake has probably arisen from the fact that the teeth 

 on the free edge are too fine to be noticed by the unaided eye, 

 whilst the ridges of which the teeth are the terminations give 

 a circularly striated appearance to the whole scale, a decep- 

 tion which is aided by the deposit of thickening layers on the 

 proximal parts of the scale, leaving thinner and therefore more 

 transparent spaces between them. In reality the ridges run in a 

 sinuously longitudinal direction, with a certain tendency to 

 confluence along a line (a, b, fig. 1) transverse to the scale, and 

 placed at a short distance from its fixed (anterior) edge. They 

 are apparently compound, separated from each other by a very 



