324 West: Phytoplankton of English Lake District. 



24. DiNOBRYON CYLINDRICUM Imhof. This colonial Flagel- 

 late is general in the plankton of all the British lake-areas. 

 It was the dominant feature of the May plankton of Crummock 

 Water, and a large proportion of the cells had formed resting- 

 spores [vide fig. 7 a). These were first described and figured 

 by Lemmermann (in ' Forschungsber. Biol. Stat. Plon,' XL, 

 1904, p. 307, fig. 3, 4). Diam. of outer wall or membrane, 

 g-11.5 /x ; length, 48-59 \i ; diam. resting spor., 13-14 /^. 



Var. DiVERGENS (Imhof) Lemm. in ' Ber. Deutsch. Botan. 

 Ges.', XVIII., 1900, p. 517, t. 19, f. 15-20. D. divergens 

 Imhof. D. SertiUaria var. undulatum Seligo. D. siihdivevgens 

 Chodat. D. divergens var. levis Garbini. 



Fig. 8. A.-E., Ceratium hirundinella O. F. Miiller. All dorsal views. 

 A., from Derwent Water; B., from Brothers' Water; C, from Winder- 

 mere ; D., from Ennerdale Water ; and E., from Ulleswater. 



F.-H., C. cornutiim (Ehrenb.) Clap. & Lachm. ; F. and G., dorsal 

 views ; H., \'entral view ; F., from Grasmere ; G. and H., from Brothers' 

 Water. All X 200. 



This variety is the most abundant of all the Dinobryons 

 in the British plankton, occurring both more commonly and 

 in greater quantity than typical D. cylindricum. The mem- 

 brane of the individual cell is very characteristic, and so is the 

 general disposition of the colony. (Consult plate VI., and text- 

 fig. 7b). The June plankton of Derwent Water consisted 

 mostly of immense quantities of this form. In some of the 

 specimens, more especially those from Stickle Tarn, the upper 

 part of the outer wall was undulate almost as in var. Schauin- 

 slandii Lemm. 



Naturalist, 



