ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 273 



layers, and hardly descends below 40 ui. Distribution is not uniform. 

 (5) Both in summer and winter there are zones of superficial expansion, 

 which are the optimum zones of development of the species. (6) In- 

 summer deeper maxima are established, more especially for the groups 

 of lower organisms. They consist of floating senile or dead organisms^ 

 (7) Horizontal distribution is uniform. E. S. G. 



Bacillariales. — C. H. Ostenfeld {Resume planktonique, 3 partie, iu 

 Bull, trim., etc., puMie par Bur. Oonseil perm, intern, pour Vexplor. de la 

 mer ; 4° Copenhague, 1913, 403-.508, 39 charts, pis. 55-93). A study 

 of the numerous records of diatoms, enumerated in the plankton lists 

 published by the International Co-operation for the Study of the Sea, 

 1902-1909. Only the true plankton forms are mentioned, omitting 

 those of doiibtful indentificatiou. Seventy-one species are recorded, 

 together with the following details of each : — (1) General features of 

 distribution and biology ; (2) distribution within the regions investigated 

 (occurrence, both geographical and seasonal : relations to the hydro- 

 graphical conditions, i.e. temperature and salinity ; anomalies in the 

 occurrence) : (3) summary, and observations still to be made. The 

 geographical distribution of the most iniportant forty-six species within 

 the area investigated are given on thirty-nine quarto charts, together 

 with the different relative quantities of each. The geographical and 

 seasonal distribution of the marine plankton diatoms of N. W. European 

 waters are now fairly well known ; but our knowledge of the biology 

 is still very poor, as also that of the life-cycle of all plankton diatoms. 

 Remarks are made on systematics an.d nomenclature, especially witli 

 regard to Ghsetoceras, of which twenty-five species are recorded. 



R. S. G. 



SchizophyceaB.— C. H. Ostenfeld {Op. cit, 509-14 ; see also Bo(. 

 Gentralbl., 1915,128, 554-5). This paper is a part of the working 

 up of the numerous records found in the plankton lists published by 

 the International Co-operation for the Study of the Sea, 1902-1909. 

 The Schizophycese occurring in marine plankton are few and mainly 

 restricted to tropical and subtropical waters, though one species of 

 Trichodesmium reaches the mouth of the English Channel in summer. 

 Certain brackish water plankton species are found in the Baltic, the. most 

 important being Aphanizomenon flos-aquee and Nodularia spumigena. 

 The former is really a fresh-water organism, but it is carried by the 

 rivers into the Baltic and neighbouring waters. Its maximum occurs 

 in late summer and autumn, but it is found all the year round. Resting 

 spores are not found in the sea, and probably a new invasion from 

 fresh-water occurs every year. Nodidaria is a brackish water form 

 which occurs on the bottom of slightly salt bays and inlets and is at 

 times carried up into the plankton. It reproduces itself vegetatively 

 in the plankton, but dies away every year, and is supplied afresh. Its 

 distribution and time of occurrence in the Baltic are tlie same as that 

 of Aphanizomenon. Anabsena haltica J. Schmidt, another brackish water 

 organism, but of less importance, has the same biologv as Nodidaria. 



E. S. G. 



u 



