MONOGRAPH OF AMERICAN SHIPWORMS. 27 



has a strong knob, from the basal portion of which a narrow blade 

 extends down through about half the length of the shell. Pallets 

 paddle-shaped, rounded at the distal end, which is surmounted by 

 two strong periostracal prongs, which form a forked tip. The distal 

 half of the outside, which is rounded, is covered by a periostracum. 

 The inside is slightly concave, the distal half also having a thin 

 brown periostracum. 



The type. Cat. No. 344665, U.S.N.M., was collected by Mr. T. G. 

 Townsend at the Shaw-Batcher Shipyard, South San Francisco, 

 California, October 5, 1920, at water line at low tide. It measures : 

 Height, 4.1 mm. ; length, 4.1 mm. ; diameter, 4.1 mm. The pallets 

 measure: Total length, 2.8 mm., of which 0.5 mm. go to the stalk 

 and 0.7 mm. to the prongs; diameter, 0.7 mm. 



The present form is the only member of the subgenus Lyrodus 

 known from the West Coast at the present time. It agrees with 

 Teredo {Teredo) heachi in having the pallets with forked prongs 

 at the tip, but in the subgenus Lyrodus^ to which the present species 

 belongs, the pallets are not cupped at the apex. It differs from 

 Teredo {T eredoys) diegenms in having the pallets tipped with two 

 prongs instead of provided with a calcareous knob. The shell also 

 differs from Teredo {Teredops) diegensis in having the auricle much 

 larger and the anterior median portion much narrower and the 

 dental ridges of the anterior part much more distantly spaced and 

 fewer than in Teredo {Teredops) diegensis. 



I identified this species for Dr. A. L. Barrows, as stated by Doctor 

 Kofoid on page 33 of the above cited report, believing at the time 

 from the scanty material at hand that it was a young stage of Teredo 

 {Teredops) diegeiisis. Additional material sent to me l)y Mr. T. G. 

 Townsend leaves no doubt that this is a distinct species belonging to 

 the subgenus Lyrodus, and I therefore take great pleasure in naming 

 it for Mr. Townsend, who has been very helpful to me in securing 

 this material, as well as material from other sources, and for illus- 

 trations. 



Subgenus Teredops Bartsch. 



1921. Teredops Baetsch, Proc. Biol. Soc. Washington, vol. 34, p. 26. 

 In the subgenus Teredops the terminal portion of the pallets ends 

 in a calcified knob. 



Type. — Teredo {Teredops) diegetisis Bartsch. 



KET TO THE AMERICAN SPECIES OF TEREDOPS. 



Pallets : 



Stalk stout floridana. 



Stalk slender diegensis. 



Shell : 



Anterior portion of median part very broad floridana. 



Anterior portion of median part only moderately broad diegensis. 



