N"o. 645] 



VERTEBR.¥. OF FISHES 



363 



served at the same locality in 1919. The data for Lepomis 

 incisor seem satisfactory (see Hubbs, 1919), but those for 

 Notropis atherinoides are less complete and more cir- 

 cumstantial. In the case of the minnow, the develop- 

 mental period is divided into three periods (A, B and C) 

 corresponding with the three subclasses into which the 

 1919 year-class has been divided. Period A followed an 

 inshore spawning migration of the mature individuals, 

 coincident with the rapid rise in temperature during 

 March ; period C preceded the withdrawal of the breeding 

 stock from the shore waters of the lake; the intervening 

 period is termed B. 



The limited field observations on the spawning and 

 developmental period for Notropis atherinoides during 

 1919 are, fortunately, strongly confirmed by a study of 



the scales. The scales of the largest specimens taken in 

 December, namely those comprising subclass I9199A, and 

 forming a distinct mode in the frequency graph (Fig. 1), 

 show a well marked nuclear area of weak concentrated 

 circuli indicative of retarded growth, followed by the 

 coarser, more regular circuli indicative of normal summer 

 growth. This initial period of retarded growth presum- 



