Mr. J. Ralfs on the British Desmidiese. 191 



Each segment is inflated at the base and attenuated upwards ; in 

 general the end is slightly dilated, and the notch is rather deep 

 but not gaping. In some specimens the sides are entire, in others 

 they are slightly emarginate. The end view is elliptic and entire 

 with the exception of the transverse notch. A transverse view is 

 longer than broad with rounded and entire ends, and the sides 

 slightly inflated in the middle. The opening which marks the 

 place where the segments are connected is small and circular. 



The empty frond is punctated. 



Plate VII. fig. 2. Euastrum didelta : a, front view ; b, side view ; c, trans- 

 verse view ; d, end view ; e, end view of terminal lobe ; /, empty frond. 



5. E. affine. Segments emarginate at the sides near the base; the 

 end dilated, emarginate, rounded at the corners, and the neck with 

 a rounded projection on each side. 



In peat-pools near Dolgelley. 



Fronds about as large as those of Euastrum didelta ; the seg- 

 ments somewhat resemble a decanter in form ; the base is broad 

 and inflated and contracted upwards into a wide neck ; the di- 

 lated end may be compared to a thick rim of a decanter, and on 

 each side of the neck is a small projection or tubercle ; the ter- 

 minal notch is deep but not gaping. The body of the segment 

 is broadly emarginate at each side ; all the lobes or projections 

 are rounded, and the sinuses shallow. 



This form approaches to Euastrum didelta, of which it may 

 perhaps eventually prove merely a variety ; but as I have gathered 

 both forms unmixed with each other, and the present plant, be- 

 sides the above characters, has protuberances on the front surface, 

 I venture to keep them separate. Although I have not seen it, 

 I suspect that a transverse view may afford additional marks of 

 distinction. 



Plate VII. fig. 3. Euastrum affine: a, mature plant; b, young frond. 



6. E. gemmatum. Segments emarginate at the sides near the base, 

 suddenly contracted into a very short neck ; terminal lobe much 

 dilated, obscurely emarginate. Cosmarium gemmatum, Breb. ; 

 Menegh. /. c. p. 221. 



p. Terminal lobe emarginate at each side. 



In peat-pools near Dolgelley ; Penzance, J.R. ; Weston Bog near 

 Southampton, Mr. Jenner. 



/3. Dolgelley. 



Fronds rather smaller than those of E. didelta, nearly three 

 times as long as broad ; each segment consists of a broad basal 

 portion, which is somewhat quadrilateral and emarginate at each 

 side, and suddenly contracted to form the very short neck ; the 

 terminal lobe has each side elongated and rounded, entire in a 

 and slightly emarginate in /3 ; the terminal notch is very obscure. 

 A transverse view is twice as long as broad, with two rounded 



