554 BULLETIN 100, UNITED STATES NATIONAL MUSEUM 



lines which are in reality the continuations of those of the middle 

 part. The posterior part is distinguished from the median part by 

 a profound constriction. It forms an immense auricle which is very 

 high and which is marked by feeble concentric lines which coincide 

 with its basal margin. The junction of the anterior and median 

 part is marked by a tumid area. Interior bluish white, the middle 

 portion is rather roughened and terminates ventrally in a very strong 

 knob. The posterior part is wing-shaped, very broadly expanded and 

 placed upon the posterior portion of the median part in such a way 

 that it projects over it as a decided shelf which is very thick at its free 

 border and contains a large cavity behind it that extends to the ven- 

 tral margin. The umbonal portion, that is, about one-fourth of the 

 length of the posterior part, is narrow and very much thickened, 

 while the rest is very broadly expanded and concave, and marked by 

 wavelike corrugations which coincide with the ventral margin in 

 disposition. There is a strong blade which extends obliquely from 

 over the umbone toward the ventral knob. The pallet is unknown. 

 We are therefore unable to give this form subgeneric or even generic 

 designation. The shell, however, is so characteristic that, for the 

 sake of completeness, we felt that the species must be recognized. 



The type (Cat. No. 311063, U.S.N.M.) was collected by the United 

 States Bureau of Fisheries Steamer Albatross Philippine Expe- 

 dition, from a piece of wood dredged at station 5269 off Matocot 

 Point, western Luzon, in 220 fathoms on fine sand and pebbly bot- 

 tom. It measures: Height, 6.3 mm.; length, 6.5 mm.; diameter of 

 half shell 3 mm. Cat. No. 312934, U.S.N.M., contains another valve 

 taken from the same piece of wood. 



