DALL: MOLLUSCA AND BRACHIOPODA. 425 
Xylophaga mexicana Da tt, n. sp. 
Shell small, short, posterior area rounded behind, concentrically marked only 
with incremental lines; median furrow wide, channelled, in the adult bounded 
behind by a flattened thread, in front the elevated margin of the channel is 
obliquely serrate by the terminations of the sagittate sculpture of the anterior 
area, which a little more anteriorly becomes very fine, so as to require strong 
magnification to bring out its character; anterior margin of the valves with a 
rectangular sulcus, from whose apex an impressed line proceeds to the umbo, 
the angulation of the sculpture resting on this line; anterior auriculation small ; 
anterior dorsal margin strongly reflected; interior smooth except for a strong 
flattish rib which extends from the umbo under the middle of the wider external 
channel; umbo much incurved ; myophore small and slender. Alt. 4.2; lon. 5.2; 
diam. about 4.0 mm. 
U. S. S. “Albatross,” station 3422, off Acapulco, Mexico, in 141 fathoms, 
mud, bottom temperature 53.5. 
Two right valves were dredged as above. 
JOUANNETINAE. 
PHOLADIDEA Turton. 
Pholadidea (Penitella) minuscula Da tt, n. sp. 
Shell extremely small, white, subequivalve, with rounded, reflected processes 
behind, that on the right valve slightly more concave and larger; posterior area 
sculptured only with incremental lines medial, sulcus shallow; anterior area sculp- 
tured with doubly arcuate paired elevated lines, more distant near the sulcus and 
more crowded anteriorly; these are angulate at a point corresponding to the ante- 
rior marginal sulcus, and crossed by sharply incised striae which break them up 
more or less into segments, especially in front; anterior dorsal margin recurved, 
with quite a space under the reflection in front of the umbo; mesoplax single, 
small, elongate; protoplax cordate, small, single; in the adult the callum com- 
pletely closes the anterior hiatus. Lon. 4.0; alt. 2.5; diam. 2.5 mm. 
Boring in the corky envelop of a large seed, dredged by the U.S. S. “ Alba- 
tross,” at station 3392, Gulf of Panama, in 1270 fathoms, hard bottom, tempera- 
ture 36°.4 F. 
That the species is adult is evident, because the anterior hiatus is completely 
closed by a well-calcified callum. It is perhaps the most minute adult pholad yet 
reported. 
Teredinidae. 
TEREDO Liyne. 
? Teredo, sp. indet. 
A tube, belonging to Teredo or Xylotrya, was dredged by the “ Albatross,” at 
station 3393, Gulf of Panama, in 1020 fathoms; but it may have sunk from de- 
cayed driftwood disintegrating at the surface of the sea. 
