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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 (PI. 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). lts 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. lts 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 

 nö figures of these parts of a species of CJithamalus have been published before, I think it 

 not superfiuous to give a few figures for the present form. 



The crest of the labrum (PI. XXVII, fig. 19) is not only hairy, but furnished with a 

 row of teeth as well. The pal pi are quadrate, with rounded edges, and are furnished with 

 numerous and partly very long hairs. 



The mandible (PI. XXVII, fig. 20) has three main teeth, the fourth is very small, 

 laterally doublé and confluent with the lower pectinated angle. 



The maxilla (PI. 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 maxilla e have the outer marsfin 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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