166 THE VOYAGE OF H.M.S. CHALLENGED 



The scuta (PL XIII. fig. 37) are triangular, but the tergal margin is much shorter 

 than the other margins; the depression for the adductor muscle is not very deep, but 

 the articular ridge is very prominent and has an arched edge. The terga (PI. XIII. 

 fig. 38) are elongate, rather narrow. The spur is not very distinctly developed. The 

 crests for the depressor muscles cannot be said to descend beneath the basal margin of 

 the valve. The articular ridge is strongly sinuous, but it is also very prominent. The 

 carina] margin is distinctly arched. 



Of the animal itself I will only give details with regard to the structure of the mouth 

 and the first two cirri. The crest of the labrum is not only hairy, but there are also some 

 fine teeth. The palpi are very broad and stout, and bear a great number of hairs, which 

 are placed along both margins, and also on the exterior surface; the hairs are different in 

 leiioth, but they have almost the same thickness. The mandibles have three normal teeth ; 

 the fourth is divided into two parts, and is situated immediately in front of the pectinated 

 inferior angle. At the inferior extremity of this angle a slightly stronger tooth is visible. 

 The maxilla have three larger spines above the notch and three smaller ones on the upper 

 margin of the notch. Behind the notch a row of spines is visible, the posterior ones being 

 smaller than the anterior. The second maxillce show a terminal lobe and a lower 

 lobe, .both furnished with numerous spines. The first pair of cirri has six segments 

 in both rami ; the second pair six segments in the one and eight in the other ramus ; 

 both cirri have the front margin of the rami covered with numerous spines, the hinder 

 margin being furnished with tufts of spines at the extremity of the segments. 



This species was taken in the Pacific, September 2, 1875, from the screw of H.M.S. 

 Challenger. (About Station 269, lat. 5° 54' N., long. 147° 2' W.) The Challenger left 

 Yeddo (Japan) about the middle of June, after a stay of more than a month in the waters 

 of Japan. Probably the specimens attached themselves in the Cypris-stage to the screw 

 when the vessel was there. 



This species is no doubt nearly related to Chthamalus stellatus, Poli, sp., and also to 

 Chthamalus antennatus, Darwin. The difference is, I think, in the form of the opercular 

 valves, which in the two above-named species, according to Darwin, are hardly 

 distinguishable from one another. In the present species the articular ridge of the scutum 

 is much more prominent, and besides, the form of the tergum is much more elongate. 

 On account of its carinal margin being protuberant, it resembles Chthamalus dentatus, 

 Krauss, but in consequence of the slightly-pointed and depending basi-carinal angle it is 

 perhaps also related to Chthamalus cirratus, Darwin. Many of the so-called species of 

 this genus resemble one another so much that one almost feels inclined to doubt the 

 correctness of Darwin's opinion when he considers them as so many different species. It 

 is, however, possible that a close examination of the groups of specimens which Darwin 

 had at his disposal would convince us, on the other hand, that the great naturalist was 

 right in the present case also. 



