28 
PATAGONIAN EXPEDITIONS : PAL/EONTOLOGY. 
The internal cast also shows a deep groove, corresponding to a heavy 
internal rib, extending back from the beak to the posterior margin above 
the umbonal ridge, and some specimens show a much fainter furrow in the 
same position on the exterior of the shell. 
On one specimen near the beak there is a small subtriangular structure 
that appears to be an accessory valve (protoplax) and indicates by its form 
that there were two of them, as in Xylophaga. 
The animal burrowed in wood, forming long more or less tortuous 
shelly tubes like those of Teredo, the surface of the tubes bearing irregular 
annular wrinkles, or lines of growth. 
Length of a medium sized specimen, 7 mm.; height, 6.5 mm.; convexity 
of both valves, 6 mm. The larger tubes measure 7 mm. in diameter and 
some of them, though broken, are over 30 mm. long. 
This species is quite similar in habit and general form to some species 
of Teredo, such as T. torulosa Stoliczka from the Cretaceous of southern 
India, but the apparent presence of a callum and of accessory valves and 
the strong internal rib prevent its reference to Teredo. In the presence 
of a callum closing the anterior hiatus, it differs also from the type of 
Turnus, but in other characters, including the supposed “ protoplax,” it 
agrees with that genus, for although described as without accessory valves, 
a specimen of the type species ( T plenus ) from the Cretaceous of Cotton- 
wood Creek, California, shows a structure precisely like that described as 
a probable protoplax in this species. The presence or absence of a cal- 
lum in the adult is considered less important than the other features de- 
scribed. 
Several fragments of fossil wood in the collection are filled with the tubes 
and these have yielded 19 more or less perfect specimens of the shells. 
Locality and position . — From mouth of canon of Rio Tarde, four miles 
east of Lake Pueyrrydon, Lower conglomerate, 300 feet below Ammonite 
bed. 
SCAPHOPODA. 
DeNTALIUM (LaEVIDENTALIUM) limatum sp. nov. 
PI. VI, Fig. 9. 
Shell rather large, slightly arcuate, with circular cross-section ; surface 
appearing smooth and highly polished, but showing when magnified very 
