ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 279 



cussion. He states that D. lenticula can be characterized with entire 

 certainty, and has no connexion with the many specific individuals 

 which have been classed with it by various authors. He gives a pro- 

 visional table of a group of Peridinieae disposed in a descending series. 

 Peridinium-Diplopsalis, according to the progressive reduction of the 

 number of plates of the carapace. 



Three Diatoms.* — J. Pavillard writes on three diatoms, Schroederella 

 delicatula H. Perag., Rhizosolenia fragilissima Berg., and Chsetoceros 

 Dadayi a new species. The first of these has a somewhat complicated 

 synonymy. The spine of the central valve and the presence of two 

 marginal " baguettes " justify its position in a new genus, as distinct 

 from Detonula as from Lauder ia. Rhizosolenia fragilissima Ost. (non 

 Cleve), R. faeroensis Ost., and R. pellucida Schroed., are one and the 

 same species. As to Chsetoceros Dadayi, it is a new species associated, 

 like C. tetrastichon, with Tintinnus inquilinus. There is in the diatomic 

 chains a sort of hereditary pre-adaptation to symbiosis, but the mechanism 

 of the association with Tintinnus is still unknown. Chsetoceros Dadayi 

 is distinguished from C. tetrastichon by the more or less atrophied horns 

 of the right side, while those of the left are much developed, thick, 

 rigid, bristling with hairs, and ending in a point. 



Plankton of the Victoria Nyanza.f — J. Yirieux has studied the 

 plankton of the Victoria Nyanza at two different times of the year, and 

 in two distant localities, Entebbe and Kavirondo. Entebbe is very rich in 

 algas, with numerous individuals. Both flora and fauna are very varied. 

 An abundance of Desmids was found in the lake. Among the diatoms, 

 Surirella and Cymatopleura take on a limnetic character. In general 

 there are found the usual lacustrine types, though many elements are 

 missing : Dinobryon, Mallomonas, Asterionella, Tabellaria, Fragilaria. 

 Rare are Rhizosolenia, Peridinium, and Ceratium. This absence and 

 rarity can only be explained after further research. 



Plankton of the Lac des Settons.J — J- Virieux writes on the 

 plankton of the Lac des Settons, which is an artificial lake, 3 km 

 broad, 20 m. deep and situated at an altitude of 600 m. The characters 

 of the plankton are intermediate between those of a lake and of a 

 marsh. The eu-limnetic types are scarce (Gomphospheeria) . The algse 

 consist of a mixture of forms well adapted to a plankton life (Stauras- 

 trum, Cosmocladiwn), and of numerous forms common to marshes. .The 

 recent age of the reservoir has not allowed the inhabitants time to take 

 on the complete lacustrine character. The author records about 

 ?>0 species, three of which are new records for France. 



* Bull. Soc. Bot. France, lx. (1913) pp. 126-33 (figs, in text). 



f Voyage de Ch. Alluaud and R. Jeannel en Afrique Orientale, 1911-12. Res. 

 Sci. Paris (1913) 20 pp. (2 pis. and 1 text-fig.). See also Bot. Centralbl., cxxv. 

 (1914) p. 349. 



% Feuille des jeunes naturalistes, ser. 5, xliii. (1913) pp. 14-17 (figs, in text). See 

 also Bot. Centralbl., cxxv. (1914) p. 263. 



