54 WEST AMERICAN SHELLS 
Figure 38 
gives two 
views of Thy- 
asira  bisécta, 
Conn. =e 
Cleft Thyas- 
ira, which was 
found in Pu- 
get Sound in 
deep water by 
Ptot2O5 78: 
Johnson. It 
has also been found in the far north. It is the 
largest species of the genus, sometimes measuring 
two or even three inches across. The figure plainly 
shows its peculiarities. 
Thyasira barbarénsis, Dall, the Barbara Thy- 
asira, resembles the last, but the beaks are more 
nearly in the center. It was formerly known as 
Cryptodon and Axinus. It ranges from Washing- 
ton to Mexico. The shell is white and chalky ex- 
ternally, and measures 17mm. in length. 
Thyasira excavata, Dall, the Sculptured Thyas- 
ira, has a thin, white shell, with a yellowish epider- 
mis. ‘The side of the shell is deeply infolded, mak- 
ing a sharp excavation. Length, 20mm. Dredged 
from deep water off Oregon, and in the Gulf of 
California. 
