No. 6.] AMERICAN MORPHOLOGICAL SOCIETY. 361 



The proportion practically coincided with the normal except 

 in the case of young females mated to old male, where a slight 

 increase in the number of males appears. 



3. Malnutrition (a result of feeding to one-half usual amount) : a very 

 marked increase in number of males ; rate of 1 76.6 males to every 

 100 females. 



4. Scarcity of males, i.e., polygamy : 20 females mated to i male, a 

 marked increase in number of males; 139.6 males to every 100 females. 



5. Conditions connected with time of year : 650 chicks hatched between 

 March 15 and May 15 gave a smaller proportion of males, 73.9 males to 

 every 100 females; while 471 chicks hatched between May 15 and July 15 

 gave a larger proportion of males, 88.4 males to every 100 females. 



It is to be understood that these figures are for a relatively 

 small number of cases ; it is hoped to extend them to at least 

 10,000 individuals. 



XXV. NOTES ON VARIATION IN THE 

 SHELLS OF PURPURA LAPILLUS. 



R. P. BIGELOW AND H. S. CONANT. 



Purpura lapillits is a species that presents great variations 

 in its diagnostic characters. It was thought, therefore, that a 

 study of its variations by statistical methods might be of value 

 in defining more exactly the limits of the species, and might 

 also bring to light facts of general biological interest. Collec- 

 tions were made at Prince's Cove and on the mainland opposite 

 Clark's Ledge, Eastport, at Kennebunk Beach, at Bass Rocks, 

 Gloucester, and at Newport. The sexes were separated for 

 each locality, and the following characters were measured : 



(i) Angle of the apex and nuclear whorls, or nuclear angle; 

 (2) angle of the apex and the last whorl, or adult angle ; (3) total 

 length ; and (4) length of spire from the apex to the poste- 

 rior margin of the opening of the shell. Record was made 

 also of the presence of (5) imbrications, (6) sutures, (7) ribs, 

 (8) teeth, (9) of the curvature of the columella, and (10) of the 

 weight. Perhaps the most obvious variations are in the color 

 and the thickness of the shell, but no satisfactory method was 



