ANATOMY AND PHYSIOLOGY OF THE WING-SHELL ATRINA 
RIGIDA. 8 
By BENJAMIN H. GRAVE, 
Assistant Professor of Zoology, University of Wyoming. 
INTRODUCTORY. 
Atrina rigida (Dillwyn) occurs along the eastern coast of America from the north- 
ern shore of South America as far north as Cape Hatteras. At Beaufort, N. C., where 
most of the observations reported in this paper were made, this species is confined to 
shallow water near low-tide mark, occasionally being exposed during unusually low 
tides. Another species, Atrina serrata (Sowerby), is found in the deeper water of the 
inlet. The largest specimen found measured 14 by 9 by 3 inches, but the average size 
is only about 11 by 8 by 2% inches. 
This mollusk is not without an economic interest and value. The black pearls 
formed in Atrina and Pinna , and produced in considerable numbers, have been used in 
the manufacture of brooches and other articles of jewelry, and there is no reason why 
they should not be used more extensively. They are usually spherical in shape and 
quite smooth. 
The pearls are not found in all specimens, but as many as ten have sometimes been 
found in a single individual. At a rough estimate I should think pearls would be found 
in about one-fifth of the individuals. This was about the proportion as regards those 
examined during the preparation of this paper. 
The byssus has been used extensively in the manufacture of various articles, such as 
shawls, caps, waistcoats, gloves, purses, etc. The following quotation from Simmonds’s 
Commercial Products of the Sea gives in a few words the extent to which the byssus 
has been used in the past, as well as its present standing as a commercial product : 
The ancients made this [the byssus] an article of commerce, greatly sought after, and the robes 
formed of it, called “tarentine,” were very much in esteem. ***** 
a Dissertation submitted to the Board of University Studies of the Johns Hopkins University in conformity with the require- 
ments for the degree of doctor of philosophy. 
I am indebted to Prof. W. K. Brooks for the suggestion that I undertake the study of the anatomy of Atrina. 
My thanks also are due especially to Prof. E. A. Andrews, under whose direction this work has been done and who has 
offered many helpful suggestions and stimulated my interest in biological study. I am indebted to the Commissioner 
of Fisheries for the use of a table at the fisheries laboratory at Beaufort, N. C., during the summers of 1908 and 1909; 
to H. D. Aller, director of the laboratory, for many conveniences while there and for assistance in procuring material; 
to Prof. G. A. Drew for counsel and suggestions; and to Prof. William H. Dali, of the Smithsonian Institution, for the 
determination of the species and the free use of his library. 
