The cirri of the fourth-sixth pairs have about the same structure. The sixth cirrus 

 has rami of 18 segments; each segment bears four pairs of spines as on the third cirrus. 

 Ca u dal appendages extremely short with a tuft of hairs at the extremity. 

 Penis rather thick, slightly swollen at the extremity, where it bears a dense tuft of hairs. 



H. M. S. "Siboga" collected this species on two different occasions: 



Stat. 251. December 8, 1899. Lat. 5°28'.4S., Long. i32°o'.2E. Depth 204 m. Bottom: hard 

 coral sand. Two specimens and four with abnormal capitula. 



Stat. 253. December 10, 1899. Lat. 5°48'.2 S., Long. I32°I3'E. Depth 304 m. Bottom: gray 

 clay, hard and crumbly. Four specimens. 



General Remark. This species comes near to P. Kaempferi Darwin in some regards, 

 in others it seems to approach P. aurantium Darwin. Gruvel who investigated numerous 

 specimens of P. Kaempferi from Cape Bojador thinks that P. aurantium is a variety of P. 

 Kaempferi. He gave a new figure of this form — it leaves no doubt, I think, that the 

 specimens collected by the "Siboga" are really distinct from it. But the three forms: Kaempferi, 

 atirantium and dubium are certainly nearly related and belong to one and the same group 

 of species. . 



Observation. The capitulum of four of the specimens collected at Station 251 is 

 more or less abnormal. They are small specimens and differ considerably from one another. 

 From the figures i,a — af, of PI. X these differences may be juclged. 



Fig. ia represents the least abnormal one. It is a small specimen, the greatest diameter 

 of the capitulum measuring 5 mm., the whole animal 6,5 mm. only. It is slightly more swollen 

 transversely than the normal specimens, the occludent margin of the scutum being more strongly 

 convex. The principal difference, however, is in the tergum being distinctly divided into two 

 parts by a line running nearly parallel with the scutal margin. 



Fig- 1 b gives the next stage of abnormality. The specimen has about the same size 

 as the foregoing: capitulum 5 mm., total length 6 mm. The division of the tergum into two 

 pieces is in this specimen more pronounced, the superior part being rounded off and overlapping 

 the inferior, especially towards the occludent side of the valve. In this specimen, moreover, the 

 carina is broken up into three parts: the largest being the inferior one, two smaller, narrower 

 parts lying between the inferior piece and the obliquely truncated basal end of the tergum. 



Fig. 1 c represents a still more advanced stage of abnormality. The original shape of 

 the tergum is quite lost, an elongate oval, calcareous plate occupying its place, the apical part 

 of which reaches relatively far beyond the occludent margin of the capitulum. The superior 

 part of the carina is divided into different little pieces of shell, one lying immediately between 

 the carina and the abnormal tergum, of which it might be difficult to say whether it belongs to 

 the carina or the tergum. The shape of the capitulum of this specimen is broader, the occludent 

 margin of the scutum still more strongly convex than in the other specimens. The part of the 

 capitulum occupied by the scutum is considerably larger in consequence. The size of this specimen, 

 i. e. the length of the whole animal was 5,5 mm., 4,75 being the length of the capitulum. 



Fig. ia? was drawn from the largest of the four specimens; it differs from the normal form 

 in other regards than the foregoing ones. In this specimen the whole shape of the capitulum is 



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