20 BULLETIN 122, UNITED STATES NATIONAL MUSEUM. 



what wavy in appearance, the waves corresponding in their lon- 

 gitudinal disposition with the basal margin of the shell. The 

 posterior median margin joins the posterior part or auricle of the 

 shell in a depressed groove. The auricle is very broad, and ex- 

 tends high up toward the umbone. It has a low, corrugated appear- 

 ance, the corrugations being concentrically disposed and correspond- 

 ing with the waves of the posterior median portion. The edge of 

 the auricle is thin and slightly reflected. Interior bluish white. 

 The junction of the anterior with the median portion is marked 

 by a tumid ridge, while the auricle is reflected over the posterior 

 median portion as a thin shelf. The umbone forms a strong knob, 

 from the basal portion of which the rather broad, irregular, flattened 

 blade extends two-thirds across the inside of the shell. The ventral 

 margin of the median part bears the usual heavy knob. The pallets 

 have a slender, somewhat sinuous cylindric stalk. The basal por- 

 tion is rather expanded. It is rounded on the outside and flattened 

 on the inner. The anterior portion narrows somewhat and is deeply 

 cupped. It is covered by a brownish periostracum, and terminates 

 in two horns. 



The type. Cat. No. 74499, U.S.N.M., and a lot of additional speci- 

 mens, were taken from piles at the guano works at Woods Hole, 

 Massachusetts. 



The type measures : Height, 5.2 mm. ; length, 5.7 mm. ; diameter, 

 6 mm. The pallet measures : Total length, 5 mm., of which 1.7 

 mm. belongs to the stalk; diameter, 1.7 mm. 



In comparing this American shipworm with the specimen of 

 Teredo navalis figured by Jeffreys in his British Conchology, Cat. 

 No. 194285, U.S.N.M., the following differential characters become 

 apparent. In the American species the auricle is gigantic compared 

 with the European, which is of only moderate size. The middle por- 

 tion of the median area is very rough, wdiile in the European it is 

 much less so. The w^avy sculpture described for the auricle on the 

 posterior median portion is much stronger in the American species 

 than in the European. The pallets of the American species expand 

 suddenly beyond the stalk, forming a decidedly concave outline, while 

 in the European species they expand only gradually, forming an 

 almost straight line. 



We have specimens of this species in the collection of the United 

 States National Museum ranging from Prince Edward Island south 

 to New York. 



