CRUSTACEA MALACOSTRACA. 



that at which the same form occurs at least as a rule and often exclusively in another sea. Certain 

 species which are found in the Kara Sea at less depths than 100 fm. are only met with in the cold 

 area of the northern Ocean at several hundred fathoms; thus Eusirus Holmii H. J. H. was founded 

 on specimens from 91 and 93^2 fm. in the Kara Sea; in the waters N. W. of Spitsbergen the Nor- 

 wegian North-Atlantic Expedition took it in 260 fm. ; in the waters between Jan Mayen, Iceland and 

 Norway the same expedition found it at two stations, the Ingolf at seven, and these nine stations 

 were at depths from 293 to 780 fm. In the Kattegat some species occur in shallower water than 

 anywhere round our northern dependencies. It may thus be of importance to know, not only the 

 least and greatest depth at which a species occurs within its territory taken as a whole, but also the 

 limits of depth for its occurrence in different parts of the same territory. Unfortunately gaps probably 

 occur in my account of some species with regard to their occurrence on the Atlantic coast of the 

 Spanish peninsula and at the Canary Isles, the reason being that the necessary literature is not avail- 

 able in Copenhagen. 



Some remarks may perhaps be added here on faunistic catalogues. The literature on the 

 Malacostraca is rich in such lists, but unfortunately several and sometimes indeed not a few of the 

 determinations in the most of these works are not to be depended upon and sometimes even demon- 

 strably incorrect. This is just the great danger in using faunistic catalogues, namely, that one cannot 

 be sure in numerous cases that the determination is correct; by carefully using several systematic 

 papers or a single large paper of an author, one gets to know the extent of his carefulness and of 

 his observing and critical abilities, and from this knowledge one may judge of the trustworthiness of 

 his determinations of species, when he has not included in these any remarks on structural features 

 from which one can to a certain extent or with certainty conclude for oneself, whether the determina- 

 tions are correct. But even the most careful and keen-sighted author does not escape on occasion 

 from making an error in determination, which often cannot be detected at all in a faunistic list. The 

 best list known to rue with numerous descriptions of new species are those in the excellent papers of 

 S. I. Smith on the Decapoda of the east coast of North America. Even the list prepared by G. O. Sars 

 on the Crustacea of the Norwegian North-Atlantic Expedition contains several errors, at least as 

 regards the Isopoda and Amphipoda, which he has corrected later in his splendid work, An Account 

 of the Crustacea of Norway. But when a author so prominent and with such detailed knowledge of 

 Norwegian Crustacea could make several such errors of determinations in a large work like that 011 

 the forms of this class taken by the expedition mentioned, confidence in the trustworthiness of faun- 

 istic catalogues must decline to a great degree. There are also various lists in which I can place no 

 confidence for a number of species, even though such lists may display many citations and thus show 

 knowledge of the literature, for the reason that this learning is not necessarily accompanied by exact 

 investigation or by critical judgment etc. My confidence in catalogues of species is constantly growing 

 less and less as the years go on, the more so as various journeys have given me the opportunity of 

 finding out very remarkable errors of determination in earlier works on examining the original speci- 

 mens. It is almost desirable that authors would be less industrious in publishing faunistic lists, 

 especially those on difficult grotips and on the fauna of a small stretch of coast, or frequent small 

 additions to older lists. 



