214 SUMMARY OF GUKRENT RESEARCHES RELATING TO 



picture. Very few species of Desmids and green algse occur, and these 

 almost disappear in summer. On the other hand, a Diatom flora 

 flourishes in spring, autumn and winter, poor in quality, but very rich in 

 quantity. In summer the Baltic fresh-waters are characterized by a 

 monotonous Myxophyceae flora, very rich in quantity, which mostly 

 ^appears as water-bloom. The author has examined waters in the 

 neighbourhood of Stockholm and finds therein both types of plankton. 

 Most of them are typically Baltic, but two contained English and 

 Norwegian species. The author maintains that this difference of 

 plankton vegetation depends on the peculiar composition of the lakes. 

 Waters in thickly inhabited districts are fouled by nitrogen-containing 

 matter, which encourages the development of Myxophycea. The Baltic 

 waters are in districts which have been built over for a long time ; while 

 the mountain waters in the highlands of England, Norway and Sweden 

 are poor in nitrogen, and are therefore not inhabited by Myxophyceae, 

 but by Chlorophyceffi. The author regards the following species as the 

 most leading features of the Caledonian plankton-formation : — Arthro- 

 ■d'^smus Incus, A. quiriferus, A. crassiis, Cosrnarium contractum var. 

 •eUipsoideum, Spondiplosium planum, Staurastrum aretiscon, S. lunatum 

 var. planctonicum, Xanthidium antilopseum, Crueigenia rectangularis and 

 var. irregularis, Quadrigula closterioides, Stichoglaa Dcederleinii, Ceraiium 

 curvirostra, and Tabellaria Jiocculosa va.r. pelagica. 



Heterodinium in the Adriatic* — J. Schiller describes the differences 

 between the genera Peridinium and Heterodinium. Two new species are 

 •described : H. crassipes, which occurs in very salt water in Dalmatian 

 waters, rarely in the high seas, never on the Italian coast waters, steno- 

 haline ; H. Kofoidi, with very transparent frustule, found throughout 

 the entire middle and south Adriatic, at a depth of 10 m., in autumn 

 and winter, strongly euryhaline and stenotherm, and, therefore^ with a 

 wide power of physiological adaptation. 



ChaBtoceros criophilus.f — L. Mangin, having studied the plankton 

 •of the Antarctic Expedition of the " Pourquoi-pas ? " and of the " Scotia," 

 finds that the true Chsetoceros criophilus Castr., has nothing to do with 

 the Arctic forms attributed to it, and he denies the presence of the true 

 v. criophilus in the Arctic zone. He gives a detailed description of the 

 species, with figures, illustrating among other points the insertioa of the 

 horns. In a later paper the author treats of the forms designated by 

 authors as C. criophilus. The G. criophilus of Gran is considered a new 

 species, to which the author gives the name of C. concavicortiis, with a 

 variety currens (Cleve). The only true C. criophilus is the species 

 •described by Castracane in the Diatoms of the " Challenger " Expedi- 

 tion, and it differs from the Arctic G. concavicornis by the mode of the 

 insertion of the horns. The latter species is most closely allied to 

 C. peruvianus, and its synonyms are : C. criophilus Joerg., G. Brightwdlii 

 ■Gran, G. borealis var. Brightivellii Cleve, and G. peruvianus Vanhoffen. 



* Arch. Protisteuk., xxxvi. (1916) pp. 209-13 (4 figs.). See also Bot. Gentralbl. , 

 •cxxxv. (1917) p. 52. 



t Comptes Rendus, clxiv. (1917) pp. 704-9 (4 figs.) ; 770-4 (.3 fig?.). 



