644 Fritsch . — Further Observations on the 
by the river, and its consequent removal from the current, 
showed a well-marked Plankton of its own. This is chiefly 
interesting because of the abundance of Melosira varians 
present, which is quite the most prominent form ; this back- 
water as it were is at present in the phase of Plankton-develop- 
ment, found in the main river about two months ago. The 
Metosira completely eclipses the species of Synedra in num- 
bers, whilst it is accompanied by a relatively abundant 
development of Fragilaria virescens. Green forms are rare 
here, some of them not being even as common as in the main 
river. The main mass of the Plankton of this backwater 
is thus constituted by Diatoms. 
(iv) Backzvater just above Shepperton (June 6, 1903). 
1 
Backwater ; 
t = i8°C. 
Main river; 
t = i8°C. 
Stephanodiscus Hantzschianus , Grun. . 
rc. 
rc. 
Melosira moniliformis (Mull.) , Ag. . . 
— 
rc. 
„ varians, Ag 
a. 
c. 
Campy lodiscus noricus, Ehrb 
— 
rr. 
Surirella biseriata, Breb 
— 
r. 
,, ovalis , Breb . 
— 
r. 
„ splendida (Ehrb.), Ktz. . . . 
rr. 
rc. 
Cymatopleura Solea (Breb.), Sm. . . . 
IT. 
r. 
Cymbella gastroides , Ktz 
r. 
— 
Amphora ovalis , Ktz 
r. 
r. 
Fragilaria virescens , Ralfs 
a. 
c. 
Synedra Acus, Ktz 
rr. 
rc. 
,, Ulna , Ehrb 
rr. 
rr. 
Nitzschia sigmoidea (Nitzsch), Sm. . . 
c. 
r. 
Pleurosigma attenuatum (Ktz.), Sm. 
r. 
rr. 
j Tabellaria Jlocculosa , Ktz 
l'C. 
— 
,, fenestrata , Ktz. ..... 
r. 
r. 
Scenedesmus quadricauda (Turp.), Breb. 
r. 
r. 
,, aculus, Meyen 
r. 
— 
Pediastrum Boryanum (Turp.), Men. . 
rr. 
r. 
„ pertusum , Ktz 
rc. 
rc. 
Eudorina elegans , Ehrb 
rc. 
— 
Pandorina morum , Ehrb 
rc. 
— 
Richteriella polychaete, Fritsch, n. sp. . 
rr. 
— 
Closterium moniliferum (Bory), Ehrb. . 
vr. 
~ 
Synura Volvox , Ehrb 
rc. 
■ — 
This backwater is of no very great length, and is sufficiently 
deep to admit of rowing all along it. The flora shows well- 
