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Half-a-dozen small specimens, attached to a piece of blackish stone, were collected in 
the Bay of Pidjot, Eastcoast of Lombok, when H. M. S. “Siboga”’ paid a visit to that island. 
The specimens were in dry condition when I investigated them; their peculiar appearance 
may be partly due to this circumstance. 
The shell was much depressed, the walls folded, sutures partly obliterated, orifice broadly 
oval (Pl. XXVII, fig. 17). 
The scutum (fig. 18, a) has the tergal margin much shorter than the other margins 
and deeply notched in the lower half near the basi-tergal angle. Occludent and carinal margins 
are both furnished with rather strong rims, the whole valve being unusually thick. 
The latter is the case in a still higher degree with the tergum (fig. 18). Its scutal 
margin is deeply notched for the reception of the broad process of the tergal margin of the 
scutum, and has a strong nearly quadrangular tooth fitting in the deep notch of the tergal 
margin of the scutum. Its apex is rounded, its carinal margin curved, the crests for the depressor 
muscle very strongly developed, its basal margin nearly straight and terminating in a small 
triangular process, which seems to represent the spur. The shape of the tergum somewhat 
resembles that of var. communis Darwin; but the scutum is quite different, being nearly equi- 
lateral in var. communis, and having the tergal margin relatively short in the present form. 
The structure of the mouth and of the cirri corresponds with Darwin’s description. As 
no figures of these parts of a species of Chthamalus have been published before, I think it 
not superfluous to give a few figures for the present form. 
The crest of the labrum (Pl. XXVIII, fig. 19) is not only hairy, but furnished with a 
row of teeth as well. The palpi are quadrate, with rounded edges, and are furnished with 
numerous and partly very long hairs. 
The mandible (Pl. XXVII, fig. 20) has three main teeth, the fourth is very small, 
laterally double and confluent with the lower pectinated angle. 
The maxilla (Pl. XXVII, fig. 21) has two larger spines above the notch and a few 
very delicate spines between these two larger ones and in the notch. The spines disposed 
along the outer edge are not very strong, those at the lower angle very delicate. 
The outer maxillae have the outer margin rounded and the inner margin sinuous. 
A strong tuft of bristles is disposed at the tip and along the outer side of this maxilla. The 
part representing the inner lobe is not prominent. 
Cirri. The first pair are situated close to the mouth; its branches are relatively 
short, with broad segments. The shorter and broader branch has five, the other, which is 
slightly more elongate and less broad, has six not very distinct segments. All the segments of 
both branches are furnished with numerous hairs, which form a continuous row along the outer 
margin of the shorter branch and dense groups on the surface of the segments. The lower 
segments of the longer ramus bear 3 to 4 short strong spines of conical shape which are 
about three times as long as broad at their basis and which are disposed on the side directed 
towards the shorter branch. 
The cirri of the second pair are slightly longer than those of the first pair. Each ramus 
has 6 segments and is thickly clothed with spines. The outer segments of both branches bear 
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