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from what it is in other species of the genus, yet these differences are perhaps not so great 

 as they give one the impression of being at first sight. In P. obliquum the teeth of the 

 labrum are triangular, approximated and of unequal size, whereas in the other species of the 

 genus they are bead-like and removed from one another. In P. eburneum, however, I found 

 the teeth on the lateral parts of the labrum sharply pointed, triangular, and in P. fissum the 

 same is the case. In P. obliquum the first-third teeth of the mandibles are finely pectinated; 

 traces of such a pectination are, however, observed in P. fissum also. In P. obliquum the 

 somewhat rudimentary cirri have short quadrangular segments and transverse rows of spines, 

 the pairs on the anterior faces being represented by a single pair only. In this regard this 

 species comes nearest to P . fissum — the difference being that the spines in the latter species 

 consist of two tufts, an anterior and a dorsal, whereas they form a more continuous row on 

 the cirri of P. obliquum. 



So far as the shape and structure of the valves are concerned, P. cburneum of known 

 species of Poecilasma is the nearest relative of P. obliquum ; with regard to the structure of the 

 body P. fissum has no doubt greater affinity to P. obliquum than any of the other species. 



7. Poecilasma cbtirneum (Hinds). PI. X, Fig. 6 — 7. 



Tri/asiuis eburnea Hinds, Voyage of Sulphur. I. Mollusca, 1844, PI. XXI, fig. 5. 

 Poecilasma eburnea (Hinds), Darvvin, Monograph, Lepadidae, 185 1, p. 112, pi. II, fig. 5. 



H. M. S. "Siboga" collected specimens of this interesting species on several occasions. 



Darwin's descriptions of the species of Cirripedia are as a rule so good that hardly 

 anything need be added. Having made acquaintance with the curious species P. obliquum and 

 having discovered its miniature terga, I was anxious, however, to investigate Hinds species 

 a-new and to compare its structure with that of my new species. 



With regard to the capitulum I found Darwin's description exact : the terga are entirely 

 wanting, the shape of the scuta and carina, the way in which the capitulum is placed with 

 respect to the peduncle etc. are entirely as üarwin has them. As to the structure of the parts 

 of the mouth, the cirri etc. little differences, however, were found and a few observations may 

 therefore be permitted here. 



The labrum has small teeth along its crest, those in the middle are bead-like; at 

 each side, however, half a dozen are sharply pointed and slightly distant from one another. 

 The hairs on the tip of the p a 1 p i are rather long, so long as to touch when the two palpi 

 are turned towards one another. The inferior angle of the m a n d i b 1 e is spine-like, the side 

 directed towards the fourth tooth bears an extremely minute tooth near the extremity - - whence 

 the angle is bifid, as Darwin says. Maxillae with two larger and a third somewhat smaller 

 upper spine, a couple of rather delicate and short spines at each side of the main notch; the 

 inferior upraised part is not straight, but forms steps, the excavations being indicated by Darwin 

 as minute notches. Second maxillae (PI. X, fig. 6) truncated, broad, nearly quadrangular 

 with rounded corners; hairs at the tip and along the inner surface rather numerous and not 

 very long. 



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