PSEUDOPODIA OF DIATOMS. 615 



On the Occurrence of Pseudopodia in the Diato- 

 maceous Genera, Melosira and Cyclotella. 



By 



J. O. Grenfell, B.A., F.G.S., F.R.M.S. 



With Plate XLI. 



The diatoms on which these pseudopodia have been found 

 do not belong, as might have been expected, to the motile, but 

 to the non-motile forms, to the genera Melosira and Cyclotella. 

 The Cyclotella is certainly C. Kiitzingiana. The Melosiras 

 belong to one or two small species which have not yet been 

 satisfactorily determined. 



They were first met with in April, in the large pond in the 

 gardens of the Royal Botanical Society of London, in the 

 Regent's Park. This gathering consisted almost entirely of 

 small isolated frustules of Melosira, with a few Cyclotellas and 

 some Archerina Boltoni.^ Later on filaments of frustules 

 of Melosira became commoner, while Archerina increased 

 enormously in number. Finally Cyclotellas replaced the 

 Melosiras, and the Archerinas vanished, 



I next met with pseudopodia on Cyclotellas at Stanstead, in 

 Hertfordshire, whither I was directed by a friend. 



Later I went to stay at Heytesbury, in Wiltshire, where I 

 found the river Wiley and the brooks full of a Melosira in 

 small isolated frustules, with long, delicate pseudopodia. Re- 

 cently I have found a good set of Cyclotellas with pseudopodia 

 in Kew Gardens, and others at Eastbourne. I infer that these 



* See Professor Lankester's description of this organism, ' Quart. Journ. 

 Micro. Sci.,' vol. xxiv, 1884. 



