506 SUMMARY OF CURUENT RESEARCHES RELATING TO 



Arctic Diatomacese.* — Cleve and Gnmow describe in detail tlie 

 diatoms collected by Nordenskiold, Kjellman, Stuxberg, and Lund- 

 strom, in the Swedish expedition to the Yenissei in 1875 and 1876, 

 and by Kjellraan in Finmark. Those from the Yenissei correspond, 

 for the most part, with the fresh-water algee of other northern 

 conntries ; while the diatom vegetation of Finmark is nearly identical 

 with that of Greenland and Spitzbergen. A large number of new 

 species are described, and special attention is paid to the characters of 

 the genera Achmanthes, Pleurosigma, AmpMprora, Nitzschia, Thalas- 

 siothrix, Podosira, and Hyalodisciis. 



Classification of Schizonema.f — A. Grunow discusses the classifi- 

 cation of the numerous species of diatoms belonging to the genera of 

 diatoms Schizonema and Berheleya, and gives the following general 

 arrangement of the former. 



Schizonema C. Ag. (Grun. emend.). Naviculas contained in simple 

 sheaths, or in those which are again enclosed in common branched 

 sheaths or masses of mucilage. A. Eamosissima Grun. LoricaB 

 with small central and terminal knots, lying close to the end, 

 transverse striae nearly parallel or somewhat radial, finely punctated ; 

 the dots so placed that they form fine but sharp longitudinal lines. 



a. Monema. One-rowed, or crowded in simple sheaths, h. Micro- 

 mega. Sheaths in large numbers in thick branched mucilaginous 

 common sheaths; not sharply separated from the previous section. 



B. Eadiosa. The loricse have delicately punctated transverse striae 

 which stand radially in the middle, and towards the ends turn 

 in an opposite direction ; the punctation of the striae does 

 not form clear longitudinal lines ; a small smooth round space 

 round the central knot ; end-knots near the end of the lorica. 

 o. Colletonema. Fresh-water forms with delicate simple sheaths ; 

 frustules in one or a small number of irregularly grouped rows. 



b. Schizonema. Marine forms with simple or compound sheaths. 



C. PsEUDO-ENCiONEMA. Loricfe similar to those of the last grouj), but 

 more strongly striated, and somewhat unsymmetrical ; end-knots, 

 especially in the longer frustules, at some distance from the apex. 



D. Pseudo-van-Heurckia. Loricae similar to those oi Navicula (Van 

 Heurchia) rhomhoides. E. Comoidia. Loricae with radial, strongly 

 punctated striation ; end-knots at some distance from the apex ; a 

 larger or smaller round smooth space round the central knot ; striation 

 much more delicate than in group C ; loricae perfectly symmetrical . 

 F. Loricae resembling Stauroneis, a thickening reaching from the 

 central knot on both sides to the margin of the lorica ; it is not, how- 

 ever, smooth, but covered with transverse striae ; when dry the thicken- 

 ing is more evident; when laid in ca.,ada balsam, only the two central 

 transverse striae are strongly marked : the punctation of the parallel 

 transverse striae forms delicate longitudinal lines. 



Under these groups are arranged and described forty-nine species, 

 with a great number of varieties. 



* Cleve, P. T., and Grunow, A., • Beitrage zur Kenntniss d. arktischen 

 Diatorn<-n ' (7 pis.). (4to, Stockholm. 1880.) 

 t Bet. Cenirulljl.. i. (1880) pp. ir)06-20. 



