Three New Species of Teredo 9 
1923, 56, p. 96). However the apophysis is shorter and 
narrower, the ventral knob smaller. The entire median 
area in Teredo johnsoni is always proportionately 
broader than in Teredo clappi. The range of variation 
of the denticulate ridges of both species is so great: that 
no constant difference can be established, but the angle ~ 
formed at the juncture of the ridges of the anterior area 
with those of the anterior-median area is always ap- 
proximately 90° in Teredo johnsoni whereas, in Teredo 
clapyi it is constantly obtuse, being rarely less than 100°. 
The pallets are very different from those of any pre- 
viously described species of Zopoteredo in that they are 
more nearly truly double-cupped, being in this respect 
more like Teredothyra. In Teredo somerst the charac- 
teristic median sinus can be seen only in the pallets of 
the very young, never persisting in the mature speci- 
mens. In Teredo clapyi it is frequently obscured or lost 
entirely in mature individuals, although always present 
in immature specimens. In Teredo johnsoni the sinus 
is constant in specimens of all ages. 
Specimens of this species have been found in the test- 
blocks placed by the Committee on Marine Piling Inves- 
tigations at the following locations: Guantanamo, Cuba; 
Port au Prince, Haiti; Fajardo and San Juan, Porto 
Rico; St. Thomas, Virgin Islands. 
This species is comparatively rare and the destruc- 
tion caused by it very slight. Frew specimens exceed 
60 mm. in total length. 
At Guantanamo, Cuba, a test-block placed in the water 
on October 1, 1922, contained specimens 20 mm. in length 
on December 30th. A special block made of shingles, 
placed in the water in April, 1923, contained several 60 
mm. specimens July 7, 1923. At Port au Prince, Haiti, 
