190 Mr. J. Ralfs on the British Desmidiese. 



Fronds large, appearing to the naked eye like small dots, ob- 

 long, three or four times longer than broad ; each segment diAided 

 into five lobes in a pinnatifid manner. The lateral lobes are broad, 

 cuneate, with a broad shallow notch. The terminal lobe is cuneate 

 and its notch closed ; the corners of all the lobes are rounded. 



The surface of the empty frond is minvitely punctate. 



Plate VI. fig. 4. Euastrum ohlongum: a, front view; b, side view; 

 c, empty frond. 



3. E.Pelta. Fronds smooth, subquadrilateral, three-lobed ; terminal 



lobe partly included in a notch formed by the ends of the lateral 



lobes. Cosmarium Pelta, Corda, Aim. de Carlsb. p. 121 ; Menegh. 



/. c. p. 222. 



In fresh-water pools. Weston Bog near Southampton, Ashdown 

 Forest, Sussex, and Fisher's Castle, Kent, Mr. Jenner ; Dolgelley, 

 Penzance. 



Fronds large, visible to the naked eye, about three times longer 

 than broad, of a quadrilateral form with rounded ends ; terminal 

 lobe cuneate, partly included between the ends of the lateral 

 lobes, rounded and emarginate, the notch closed ; the segments 

 of the frond are very broad, three-lobed, or rather each segment 

 has a subquadrate base and a terminal lobe. The basal portion 

 is not attenuated, and each lateral margin has a broad shallow 

 notch or sinus, in which there is sometimes a slight intermediate 

 rounded projection. 



The colouring matter is dark green with large scattered gra- 

 nules ; but the margin of the frond is generally colourless. 



The surface of the empty frond is minutely punctate. 



Plate VII. fig. 1. Euastrum Pelta : a, front view ; b, side view ; c, empty 

 frond. 



** Terminal lobes exserted and connected to the basal portion by a neck- 

 like contraction of the segment ; the corners of the lobes rounded. 



4. E. didelta. Segments inflated at the base and constricted up- 

 wards ; the end scarcely dilated ; the base is entire or slightly 

 emarginate. Heterocarpella didelta, Turp. Mem. p. 295 (1828). 

 Heterocarpella polymorpha, Ktz. Synop. Diatom, in Linnsea 1833, 

 p. 70. fig. 82 (some figures only and those not good). Euastrum 

 ansatum, Ehr. Infus. p. 162. tab. 12. fig. 6; Pritch. Infus. p. 196. 

 Cosmarium didelta, Menegh. /. c. p. 219. 



In fresh- water pools, probably common, near Southampton. Not 

 uncommon in Sussex, Mr. Jenner ; Henfield, Mr. Borrer ; Cheshunt, 

 Mr. Hassall; Barmouth, Rev. T. Salivey. Carnarvon, Dolgelley, near 

 Carmarthen, and Penzance. 



Fronds about three times as long as broad, scarcely visible to 

 the naked eye ; the segments have some resemblance to a de- 

 canter, especially when dilated at the end. The entire frond may 

 also be compared to the figm-e of the bones in the knee-joint. 



