56 THE AMERICAN NATURALIST. [Vol. XXXVIII. 



the more subject to strain and injury from its size and posi- 

 on. What is meant by "position" will be explained in the 



paragraph on the relationship of the valves to the shape of the 

 mouth. 



In the majority of species examined, papillae are found on the 

 valves. These papillae vary widely in size and arrangement. 



They may be in almost regular rows, scat- 

 tered, cover the whole valve or only a part 

 of it, even, as in Cy no scion ncbiilosus, run 

 back among the teeth. They may be 

 coarsely setiform, flattened, rounded, on a 

 stalk or, in one case, of a circumvallate 

 appearance. (Figs. 5 and 6.) In some cases 

 the papillce are fine and closely arranged m 

 rows, giving the appearance of short vertical 

 rows or folds. (Fig. 5^.) These are easily 

 rowrsTtha/ihe" ret""^ distinguished from the true folds found on 

 brVnumbef'oVsmrii some valvcs. Thcsc papillae at first appeared 

 thickenings or folds. elougatcd papillus but proved to be 



as described. In Ambloplytes gnmiens are found rugae sur- 

 mounted by small papilla. 



A third kind of valve has been mentioned as being a modifica- 

 tion of either the crescentic or U-type. The writer was for a 

 long time greatly perplexed because many of the Cypnnidae 



