2 4 9 



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 ter gum 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, b and d) and almost straight in the specimen from 

 Station 105 (PI. XXVI, fig. 2, b and d). On the latter, the scutal margin of the spui- 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. lts 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 1 2 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, I call the attention to the following points: 



Mouth. Labrum somewhat thicker than in the genus Ba/anus, but it cannot be said 

 to be bullate. No tracé 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 (PI. XXVI, fig. 8 — 10), and indistinctly doublé crowned (PI. 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 doublé 

 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 (PI. 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 doublé that 

 between 2 and 3, or 3 and 4. In one specimen, the space between the 4 th tooth and the inferior 

 angle is furnished with two additional pointed teeth; the dorsal or upper margin of the 3" 1 

 tooth bears in this specimen, moreover, a secondary tooth. In the second specimen (PI. XXVI, 

 fig. 11*) the lower margin of tooth 4 is furnished with an additional tooth. In the third, there 



121 



SIISOGA-EXPEDITIE XXXI 6. 32 



