The Nut Shells 



tended, dilated itself into two lateral flaps. Using this expanded 

 disk as an anchor, the mollusk pulls the shell down toward it. 

 Now the flaps close, forming a wedge-like cutting edge by which 

 the mud is penetrated still deeper, and again the flaps dilate, 

 and the shell is drawn down. In a second of time the Yoldia 

 burrows several inches. Cormorants and flounders are its chief 

 enemies. When out of its element the danger is greatest. On 

 the sand Yoldia often leaps at surprising angles in a frantic at- 

 tempt to get back to the mud covert. Length, i to 3 inches. 



Habitat. — New England to Cape Hatteras, Norway, Pacific 

 coast. 



The Broad Yoldia (Y. thraciceformis, Storer) shaped like 

 the blade of an axe, has a diagonal crease from the pointed beak 

 to the ventral angle of the posterior margin of the shell. The 

 surface is dark olive green. Length, 2^ inches. Height, i J inches. 



Habitat. — New England coast. 



Y. sapotilla, Gld., is like a half-grown limatula in outline, 

 though narrowed less behind. The fragile valves are trans- 

 lucent, and coated with a glossy green epidermis. The lining 

 is pearly white, with a triangular cartilage cavity, and nearly 

 twenty sharp teeth on each side. Length, scarcely i inch. 



Habitat. — Long Island northward, Alaska. 



383 



