52 THE NAUTILUS. 



EESULTS OF A STATISTICAL STUDY OF VARIATION IN THE BLUE 



SHELLS OF PECTEN NUCLEUS IRRADIANS FOUND AT 



ATLANTIC CITY, N. J. 



BY HAROLD S. COLTON. 



Upon the beach of the Atlantic shore of New Jersey are 

 found dead shells colored blue by clay particles infiltered 

 into the shell. These shells have obviously been buried in 

 the mud or clay of the bottom, out of which they have been 

 washed by the surf. 



In collecting shells from along the beach at Atlantic City 

 in 1904, the author fancied that the blue Lunatia heros dif- 

 fered in shape from the uncolored ones. 



Not having sufficient material with which to base a con- 

 clusion, he returned in the Spring to Atlantic City to collect 

 Lunatict: Although in January they were abundant, now 

 not a single one could be found. At once it was seen that 

 Pecten would be a much more favorable form on which to 

 work, as it was abundant and the ribs of the shell would be 

 easy to count, therefore a few hundred of white and blue ones 

 were collected. 



In the course of time the writer happened to mention to 

 Dr. E. F. Phillips, the present chief of the Bureau of Api- 

 culture at Washington, on what material he was working. 

 Dr. Phillips became interested, and in 1905 a joint trip to 

 the coast was made and over five hundred blue right valves 

 of Pecten were collected near Ventnor. 



The ribs of these were counted, applying the arbitrary 

 rules of Davenport (1900). The number of ribs of each 

 shell was counted independently and compared. When there 

 was a difference of opinion the ribs were recounted, and no 

 record was made until both agreed. 



This study was not completed and therefore not published. 

 While sufficient blue ones were at hand, not enough white 

 ones (representing the form of Pecten now living) were col- 

 lected for comparison. However, in looking over the results 

 it seemed that it might be of interest to publish them as they 



