249 
one extending over the middle of the valve is somewhat more distinct, the other, at a little 
distance from the tergal margin, is faint. Basal margin slightly sinuous. On the inner surface 
the articular ridge is not very prominent, the depression for the adductor muscle is very super- 
ficial, and that for the depressor muscles represented only by a very shallow excavation. 
The tergum is somewhat narrower than the scutum; the growth-ridges are distinct, 
narrower and-less prominent, however, than those on the scuta. The scutal margin is straight, 
the carinal margin feebly curved, the basal margin distinctly hollowed out in the specimens 
from Stations 59 and 251 (PI. XXVI, fig. 5, 6 and @) and almost straight in the specimen from 
Station 105 (Pl. XXVI, fig. 2, 6 and ¢). On the latter, the scutal margin of the spur is 
-) 
at a very short distance only from the basi-scutal angle, this distance being a trifle greater in 
the specimens from Stations 59 and 251. On the inner surface the articular ridge is rather 
prominent in the upper part, the crest for the depressor muscles, although not very prominent, 
is well developed. The apex of the valve develops into a very minute beak, which is a little 
more prominent in the specimen from Station 105. 
The size of the specimens can be judged from the following: 
the specimens from Station 105 are high: the largest one measures 13 mm. at the 
one side, and 6 mm. at the other. Its greatest diameter at the basis is 10 mm. 
the specimen from Station 59 is 8 mm. high, and the greatest diameter of its basis is 12 mm. 
one of the specimens from Station 251 is 7 mm. high, and the greatest diameter of its 
basis is 12 mm. 
As regards the structure of the animal's body, | call the attention to the following points: 
Mouth. Labrum somewhat thicker than in the genus Aa/anus, but it cannot be said 
to be bullate. No trace of notch, the upper margin being only very superficially ‘hollowed 
out. This margin is armed with a row of from 45 to 60 small knob-like teeth. These teeth 
are of an irregular shape: they were short, conical with the apex blunt in the specimen 
from Station 251 (Pl. XXVI, fig. 8—r1o), and indistinctly double crowned (Pl. XXVI, fig. 7) 
in that from Station 105. 
Palpi of elongately-oval shape, with the free extremity rounded. The upper margin is 
furnished with numerous short hairs, the outer surface with numerous longer ones, especially 
near the lower margin and towards the free extremity. The latter hairs form a distinct double 
row along — but at a certain distance from — the lower margin, extending in one of the 
specimens over three-fourths of its length, or, as is the case in another specimen, almost over 
the whole length of the palpus. The outer surface is, moreover, furnished near the distal 
extremity, with groups of extremely small hairs or ciliae. 
Mandible (Pl. XXVI, fig. 11) has 4 sharply pointed teeth, diminishing in size from 
the first to the fourth, and an inferior angle terminating in 2 or 3 teeth, one of which is 
somewhat stronger. The distance between the extremities of teeth 1 and 2 is double that 
between 2 and 3, or 3 and 4. In one specimen, the space between the 4 tooth and the inferior 
angle is furnished with two additional pointed teeth; the dorsal or upper margin of the 3" 
tooth bears in this specimen, moreover, a secondary tooth. In the second specimen (Pl. XXVI, 
fig. 11*) the lower margin of tooth 4 is furnished with an additional tooth. In the third, there 
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SIBOGA-EXPEDITIE XXXII 4. 32 
