ZOOLOGY AND BOTANY, MICROSCOPf, ETC. 63 



upper surface of the valve, and extending to, and closely surrounding 

 the primaries." The structure is exceedingly faint and minute, but the 

 author feels convinced that it really exists. 



Phytoplankton of the Thames.* — F. E. Fritsch gives a preliminary 

 note on the result of his investigations made during six separate days in 

 July and August of last year. The portion of the river examined ex- 

 tends from Kew to Cookham, and the samples were collected from a 

 rowing-boat by means of an ordinary funnel-shaped net of fine gauze,, 

 having the lower narrow end attached to a glass tube. The quantity of 

 plankton organisms decreases steadily down the river, and at Kew, 

 where the tidal influence is felt, the desmids and pediastrums are either 

 dead or dying, while many of the diatoms consist of mere empty 

 frustules. The author attributes this to the influence of the brackish 

 water, which enables purely marine species {Coscinodiscus radiatus, 

 Surirella ovata, and Rhaphoneis Rhombus) to exist at Kew. Diatoms, 

 play an important part in the upper reaches examined, the proportion at 

 Windsor and Maidenhead being about 20 to 1. The commonest forms 

 are Fragilaria virescens, Melosira varians, M. moniliformis, Pleurosigma 

 attenuatum in the surface layers, species of Surirella, and in parts 

 Gampylodiscus noricus. Among green algae the most common forms 

 were Pediastrum Boryanum and P. pertusum, Closterium moniliferum,, 

 Cosmarium margaritiferum, and Scenedesmus quadricauda. Species of 

 Cyanophycese occur more frequently in the lower parts of the river, the 

 commonest forms being Microcystis protogenita and M. marginata. No 

 Peridiniaceas were observed. 



A table is given in which are enumerated fifty-four species and five 

 varieties, together with their distribution and the relative number of 

 individuals found. 



Variations-Statistics as applied to Plankton-Diatoms.f — P- 

 Vogler writes a preliminary note on the importance of applying this 

 method of investigation to plankton. He expresses his results in 

 curves, and is of opinion that by this method only can a true concep- 

 tion be formed of the dimensions of a given species. He maintains 

 that average measurements are of no value. He has devoted five years 

 to this research. 



Diatomacese of the Hull District.!— F. W. Mills and E. H. Philip 

 publish an illustrated list of the diatoms occurring in the neighbour- 

 hood of Hull — to the number of about 600 species and varieties, which 

 is a considerable advance upon the lists published by G-. Norman in 

 1859 and 1865, which contained about 400 and 480 species respec- 

 tively. The present list in fact represents nearly half the species that 

 are found in the British Isles. In what is here called the Hull district 

 are included places within reach of a half-day excursion from Hull. 

 Each species and variety is figured. Most of the figures have been 

 taken from Schmidt's Atlas, Van Heurck's Synopsis, and other standard 

 and minor works ; but some have been drawn specially. The nomen- 

 clature and classification are mainly those which have been adopted by 



* Ann. Bot., xvi. (1902) pp. 576-84. f Flora, xci. (1902 , > pp. 380-3. 



X Trans. Hull. Sci. and Field Nat. Club, i. (1901) p. 157 (17 pis.). 



