SEXUAI< DIMORrHISM 165 



2 2. PlimpjEr: Pract. org. and biochemistry, p. 390, 191 7. 

 23.. True & Harvey: Absorption of Ca salts by squash seedlings. 

 Brooklyn Bol. Card. Mem. t. I., pp. 502-13 1918. 



24. Robert (MellE Th.) Le role physiologique du Ca chez les v^getaux. 

 Rev. gen. sc. p. 108, 191 7. 



25. RussEl: Part played by colloids in agric. pheno. Rept. Brit. Ass. 

 Adv. ^Sc. p. 75, 1919. 



26. WedEkind & Rheinboldt: Ber. V. 52 (B) pp. 1013-21, 1919; 

 anal, in J. Client. Sac. Abst. i. i. p. 270, July 1919. 



Sexual Dimorphism and Some of Its Correlations in the Shells of 

 Certain Species of Najades. 



BY N. M. GRIEK, TH. D. 



I. — Introductory. 

 Before Ortmann's discovery that the sex of Najades could 

 be readily learned from associated peculiarities of gill structure, 

 (4, 5,), systematists had only general information — of the type 

 later to be compared in this paper — from which to identify the 

 sex of a mussel when glochidia were absent. Hazy, (2), and 

 Israel, (3), were able to distinguish the sexes of certain European 

 species by such characters as relative length, height, and inflation. 

 Israel, particularly, found associated with sex, certain colors of 

 the epidermis of the shell. The investigations of these latter 

 writers extended only to 3 species, none of which are closely related 

 to those dealt with in this paper, and their original work never 

 seems to have been followed up. In addition there occur in the 

 papers of American investigators from time to time, scattered 

 references to the sexual dimorphism of certain species based on 

 some morphological feature of the shell. Such, however, are either 

 not concerned with the species we are interested in, or are already 

 summarized by Simpson, (6), or Walker, (8), whose information 

 later will be brought out. 



II. — Problem, Method, and Material. 



While pursuing another investigation on the comparative 



morphological characteristics of certain mussel shells inhabiting 



the Upper Ohio Drainage and their corresponding ones in Lake 



Erie, (i) the writer obtained data of the type indicated, which he 



