1894- SOME NEW BOOKS. 311 



five fascicules of text include memoirs by different specialists — on 

 the Echinodermata and Mollusca, by Dr. Petersen himself; on the 

 Cephalopoda, by Dr. H. J. Posselt ; on the Polyzoa, Annulata, 

 Coelenterata and Sponges, by Inspector Levinsen ; on the Crustacea 

 Malacostraca, by Dr. Meinert ; on the Diatoms, by Professor Cleve ; 

 and on the Bottom Deposits and the Hydrography of the Kattegat, 

 by Dr. Rordam. 



Turning first to the chemical and physical portions of the work, 

 we notice that the greatest percentage of calcium carbonate is found 

 in the deepest part of the Kattegat, perhaps in correlation with the 

 saltness of the water, while the deposits from the bottom of the 

 Baltic contain little, if any, of this substance. It appeared that 

 during the three years (1884-86) in which the observations were 

 made, the saltness of the water in the Kattegat increased, while at 

 the same time the mean temperature diminished. This result is 

 confirmed by independent observations from other sources, and is 

 attributed to an unusual prevalence of N. and N.W. winds during 

 those seasons. These facts are shown very clearly by a plate con- 

 taining nine little maps. 



The account of the Echinodermata and Mollusca by Dr. Petersen 

 need not be noticed at length here, except for the purpose of calling 

 attention to the admirable series of 26 maps by which the distribution 

 of the various species is illustrated. No new forms are here described, 

 tliough some additions to the Danish fauna are recorded. The Mollusca, 

 in particular, have already been discussed by the same author in an 

 elaborate thesis published about five years ago.^ The section dealing 

 -with the Cephalopoda by Dr. Posselt is not merely an account of the 

 few taken by the " Hauch," but is virtually a systematic monograph 

 of the Danish forms, and contains some novel information of great 

 importance. Dr. Meinert's report on the Malacostracous Crustacea 

 is a very important piece of work, being in fact a revision of the Danish 

 fauna, so far as this group of animals is concerned. The number of 

 species recorded is increased from 177 to 253, and nine new species 

 are described, of which three are referred to new genera. The 

 memoir is illustrated by fourteen maps and two copper plates. 

 Inspector Levinsen has dealt with the Porifera, Polyzoa, Hydroida, 

 and Anthozoa, and in regard to the first three of these groups has 

 given us a complete account of the Danish forms, with a very con- 

 venient dichotomous key for their identification. 



The whole work is completed by a discussion of the general results 

 by Dr. Petersen, which he has considerately printed both in Danish 

 and English ; this is naturally the most important section of all and 

 some account of its more salient features must be attempted. The 

 bottom of the sea is covered with three kinds of deposits, stones, 

 sand or gravel, and clay or ooze, the last of which occurs only in the 

 deepest places and is the most unfavourable for animal life. As to 

 vegetation, about half the Kattegat and nearly all the Skagerack are 

 destitute of it, and, next to the inshore waters, the richest places are 

 the protected situations in the Kattegat. The salinity, too, increases 

 with the depth, though it varies greatly with the seasons, the melting 

 ice in the Baltic being, perhaps, the most important factor in this 

 connection. As might have been expected, the temperature is most 

 variable in the inshore waters, where it reaches 19-23° C, and least 

 variable in the Skagerack, the deep eastern Kattegat being inter- 

 mediate in this respect. 



1 Petersen, " Om de skalbrerende MoUuskers Udbredningsforhold i de danske 

 Have indenfor Skagen," 8vo., pp. viii., 163, map, Kjobenhaven : 1888. 



