256 
THE VOYAGE . OF H.M.S. CHALLENGER. 
surface of the mandibles (Fig. 25) presents the aspect of a bivalve shell {e.g., Tellina), 
only the hinge is posterior. It is deeply coloured with blackish pigment, and veined. 
The halves of the mandibles do not seem to have been ankylosed. Three characteris- 
tically symmetrical horny plates (two lateral and great dental) are visible on each side 
of the ventral surface (Fig. 23), and the angles of the posterior (great dental) are distinct. 
As usual in the group, the first two segments (buccal) are bare. The anterior feet 
are small, but, as mentioned, gradually increase in size from before backward. At the 
tenth foot the posterior lobe is proportionally large, slanting from its somewhat straight 
upper border abruptly downward and inward. Only the upjDer bristles remain, and they 
are winged, with rather elongated tapering tips. There is a slight indication of a dorsal 
papilla, but it does not attain a noteworthy size. 
Fig. 25. 
Fig. 23. — Maxillte and dental plates of Liwihriconereis heteropoda, from the dorsum ; x 12 diameters. 
Fig. 24. — Dental plates of Lumhriconereis heteropoda, from the ventral surface ; x 12 diameters. 
Fig. 25. — Mandibles of Lumhriconereis heteropoda, from the dorsal aspect ; x 12 diameters. 
At the thirtieth foot the posterior lobe more nearly approaches the anterior in size, 
and the bristles pass out between them. The anterior is rounded dorsally, whereas 
the posterior forms an angle a little less than a right angle superiorly. The bristles 
are in about four groups, the upper having the longest, and the third the shortest tips. 
All have wings. On the dorsum near the base of the foot is a very distinct papilla 
(PI. XXXVII. fig. 2). 
The fiftieth foot is similar to the foregoing, except that the tips of the bristles are 
shorter, and that a few hooks have appeared amongst them. Toward the eightieth foot 
the posterior lobe becomes greatly developed superiorly, so as to have a considerable 
triangular area elevated above the foot. A single group of two or three slender bristles, 
reaching very little beyond the tips of the hooks (the second group from above), alone 
