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 rarrii somewhat more unequal than in second cirrus, of 8 to 10 

 and 9 to 1 1 segments. No tracé of teeth on inner face of segments of this cirrus. 



F o u r t h to s i x t h pair. Number of segments only slightly different : increasing from 1 9 

 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 (PI. 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'.4 S., Long. i32°o'.2E. Depth 204 ra. 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. I32°I3'E. Depth 304 m. Bottom: grey 

 clay, hard and crumbly. Numerous, most of them small specimens attached to 

 'the arms, cirri, etc. of a Pcntacrinus. 



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 Hcxclasma 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 WELTNER, W., Die von Dr. Sander 1883 — 85 gesammelten Cinipedien. Aichiv fiir Naturgesch. LUI. S. 9S — 117. Taf. 

 III— IV. 1887. 



2 Grvvei, A., Cirrhipèdes des Expéditions du Travaüleur et du Talisman. 1902. 



104 



