52 



exceeding half the length of the anterior division, genital segment very short, 

 2nd segment large and tumid, 5th segment very small; caudal rami mobile and 

 generally spread out. Anterior antennae with well-marked, band-like, sensory 

 appendages on the proximal part, 8th joint about the length of the 4 preceding 

 ones, and composed of several coalesced articulations, outer half of the antennas 

 very slender. Last pair of legs, when reflexed, scarcely reaching beyond the 

 middle of the urosome; both legs of about the same length, rami of the left one 

 nearly as long as the 2nd basal joint, and slightly incurved. 



Colour not yet ascertained. 



Length of adult female about 5 mm., of male 4y 2 mm. 



Remarks. This form was first described by Th. Scott from a solitary, 

 somewhat defective female specimen, found in a plankton-sample taken off the Sao 

 Thome Islands in the Gulf of Guinea. Apparently the same species was recorded the 



4f 



following year by Dr. Giesbrecht from the Pacific, under the name of Scolecithrix 

 cristata. Neither of these statements had come under my notice when I was 

 examining the plankton-material from Nansen's Polar Expedition. Indeed, I could 

 not, at that time, have imagined, that any of the polar forms were to be sought 

 for among species collected in the tropical parts of the ocean. Recent investiga- 

 tions have, however, proved that pelagic organisms may occasionally be carried far 

 from their true home by submarine currents; and therefore a thorough acquaintance 

 with those from other tracts of the oceans is indispensable in the determination 

 of such organisms. 1 cannot, indeed, find any essential difference between the 

 northern form and those observed by Th. Scott and Dr. Giesbrecht; and I am 

 therefore inclined to believe that all these 3 forms belong to one and the same 

 species, in spite of their widely remote occurrence. 



The present species may be easily recognised, at any rate in the female 

 sex, by the peculiar, helmet-shaped crest on the frontal part. The caudal setae are 

 very brittle, and it is rather unusual to meet with a specimen having them all 

 uninjured. In the specimen examined by Th. Scott they were all broken at the base, 

 a. -1 in the greater number of specimens collected during Nansen's Polar Expedition, 

 they were also more or less defective. It is owing to this circumstance that 

 they have not been correctly figured in my account of that Expedition. I have 

 subsequently convinced myself that, as in other Scolecithricidse, only 4 such setae 

 in reality occur on each caudal ramus, the 5th (outermost one) only being present 

 in quite a rudimentary condition, as a minute hair. The extremely delicate 

 terminal appendages of the anterior maxillipeds are also easily damaged, and their 

 peculiar structure was not clearly seen in the polar specimens at first examined. 



