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on the inner part of the surface of the inner lobe not much stronger and indistinctly feathered. 
The whole maxilla short and broad, the two lobes, however, very distinctly developed. 
Cirri. First pair has the two rami very unequal and consisting of respectively 6 and 
10 segments in the three specimens examined. The segments of the shorter ramus are slightly 
swollen, rounded at their inner face, they cannot however be said to be protuberant. On the longer 
ramus the hairs disposed on the segments are directed parallel to each other and to the 
longitudinal axis of the ramus. Those on the shorter ramus stand off transversely. On the tip 
of the last segment of the shorter ramus, a few stronger spines are observable,.and on that of 
the longer ramus a couple of very long, indistinctly feathered, spine-like hairs. 
Second pair has slightly unequal rami, of 6 to 8 and 7 to 9 segments. 
Third pair has the rami somewhat more unequal than in second cirrus, of 8 to 10 
and 9 to 11 segments. No trace of teeth on inner face of segments of this cirrus. 
Fourth to sixth pair. Number of segments only slightly different: increasing from 19 
in the fourth pair to 22 in the sixth. These numbers, however, could not be so well determined 
in all the specimens, as the tips of several cirri were broken off. Greatest number of pairs of 
spines seen on the inner faces of the segments: 4 (Pl. XXIV, fig. 10). On the exterior 
surface, close to its upper margin, each segment bears a group of usually three hairs, two 
of which are as long as the segment, the third being shorter. ; 
Penis, long, as long as the cirri, or even longer, growing gradually narrower towards 
the extremity. Hairs on the surface very few, a few more at the extremity. 
This species was collected by H. M.S. ‘Siboga’’ at two Stations, viz.: 
Stat. 251. December 8, 1899. Lat. 5° 28'.4S., Long. 132°0'.2 E. Depth 204 m. Bottom: hard 
coral sand. (The trawl brought up pieces of grey clay, and manganese nodules, 
the interior of which consisted of dry clay). Two groups of specimens. 
Stat. 253. December 10, 1899. Lat. 5° 48'.2S., Long. 132° 13’ E. Depth 304 m. Bottom: grey 
clay, hard and crumbly. Numerous, most of them small specimens attached to 
the arms, cirri, etc. of a Pentacrinus. 
General Remarks. This deep-sea species is, I think, especially remarkable by the 
structure of its mouth. It is a very distinct species, as shown by the shape of its shell and its 
opercular valves. But, it occupies a place of its own by the structure of the labrum, which has 
no notch. In this respect it approaches those deep-sea species that are characterised by the 
absence of radii as well, and which for this reason I think best considered as forming a new 
genus, for which the name //exe/asma is proposed in this Report. 
Genus Acasta Leach 
Darwin (1854) knew of nine species of this genus, and four species, so far I know, 
have been added to this list in the 58 years since elapsed. The new species are: 
Acasta scuticosta Weltner', 1887, from Carthagena (Spain). 
Acasta striata Gruvel*, 1901, Atlantic Ocean, depth 400 m. 
1 WetTNER, W., Die von Dr. SANDER 1883—85 gesammelten Cirripedien. Archiv fiir Naturgesch. LIII. S. 98—117. Taf. 
III—IV. 1887. : 
* Gruvet, A., Cirrhipedes des Expéditions du Travailleur et du Talisman. 1902. 
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