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palps, and by the palp of the 1st pair of maxilla3 being uniarticulate. In 

 the first of these characteristics it agrees with the genus Probolvum, whereas 

 in the second it differs from both these genera, and approaches the genus 

 Crcssa of Boeck. Another characteristic, quite peculiar to the present genus, 

 maj' be added, viz., the nearly complete coalescence of the basal lobes of 

 the maxillipeds. The genus comprises numerous species, most of which would 

 seem to be restricted to the Northern Oceans. As to the species of Mctopa 

 described by the Rev. Mr. Stebbing from the Challenger Expedition, I am 

 somewhat in doubt about their true position, since the palp of the 1st pair 

 of maxillae is represented as biarticulate, and the basal lobes of the 

 maxillipeds as not coalesced; this is at least not the case with any of the 

 northern species examined by me. The specific distinction is, in this genus, 

 connected with quite peculiar difficulties, owing both to the small size of 

 the animals, and to the often very pronounced sexual difference. Moreover 

 some species are so very nearl3' related as to be scarcely distinguishable 

 from each other without a very close examination. It may thus be easily 

 understood, that our knowledge of the species has, as yet, been very imperfect, 

 and that until lately distinct species have been confounded with each 

 other or wrongly determined. In making out the Norwegian species of 

 this genus, I have mj^self had a great advantage over most other authors, 

 in so far as I have been enabled, during my numerous voyages, not only 

 to bring together a vast material for investigation, but also to examine 

 most of the species in the living state. Such an examination is very 

 useful; for in the living animal the specific characteristics generally 

 appear far more distinct than in specimens preserved in alcohol, and often 

 even the coloration of the body alone will suffice to identify at once the 

 species. In Boeck's work onl3- 5 species of this genus were recorded as 

 occurring off the Norwegian coast. In the following pages, I propose to 

 describe no less than 21 Norwegian species, 8 of which are now for the first 

 time established. Moreover 2 arctic species were a long time ago described 

 by Kroyer as LeucotJioe clypeafa and glacialis, and more recently, Dr. Hansen 

 has added 3 new species from Greenland, 31. gy0nJandica, latimana and 

 can'nata: finally, a species, HI. a-qrieonii.^, was described by the author from 

 the Norwegian North Atlantic Expedition. 



