692 THE AMERICAN NATURALIST. (VoL. XXXIX. 
mentioned he suggested that between the shell wall and the 
buttress which supports the hinge in the dorsal valve there is a 
cavity. With the growth of the shell and the buttress this 
cavity is prolonged ; at times it is filled in part with shelly mat- 
ter and at others it persists as a tube running up with the curve 
of the umbo, one on each side of the pseudodeltidium. If these 
tubes remain empty and the umbo is sufficiently abraded, they 
will appear on the surface of the shell as two little holes. An 
abrasion to this extent is very unusual; the nearest approach 
to it noticed outside of this specimen was in Teredratula harlani 
Morton where the former cavities though filled with shelly 
- growth, yet showed faintly where weathered. 
This specimen and two other pedicle valves of the same spe- 
cies were collected by Professor W. O. Crosby of Massachusetts 
Institute of Technology in the summer of 1904; they were found 
on the beach at high tide at Kayak Village on Wingham Island, 
Controller Bay, Alaska. They are now in the collection of the 
Boston Society of Natural History, catalogue numbers 449 and 
450. 
The writer is indebted to Professor W. H. Dall of the United 
States National Museum and Professor Charles Schuchert of 
Yale University for the identification of this peculiar form. 
MASSACHUSETTS INSTITUTE OF TECHNOLOGY. 
