Mr. J. Ralfn un the British Desmidicjc. 155 



suborbiciilar frond ; the sides arc rounded and have no processes. 

 The end view is l)luntly triangular, with convex sides and rounded 

 angles. In both views the frond is copiously furnished with 

 scattered apiculi ; when it is young these are merely rough jjoints, 

 but in the mature i)lant they resemble short hairs or ))ristles. 

 The former state may be mistaken for Staurastrum tricorne by 

 those not familiar with that plant, but the convex sides in the 

 end view distinguish -S'. muricatum at all stages of its growth. 



In this and the two preceding species, as the segments are not 

 much t^^^sted, the angles only of the adjacent segment are seen 

 in the end view ; they also agree in having rounded angles which 

 are not prolonged into processes in either view. 



At Dolgelley I once gathered the conjugated state of this spe- 

 cies before the sporangium was formed. 



Plate XI. fig. 1. 6'. muricatum : a, front view ; b, end view ; c, fronds 

 conjugated; d, empty frond; e, front and end view of variety, 



7. S. tricorne, Mgh. Fronds rough ; end view triangular with con- 

 cave sides and blunt entire angles. Menegh. /. c. p. 225. Bina- 

 tetla tricornis, Breb. Alg. Fal. p. 57 (1835). Desniidium hexaceros, 

 Ehr. Infus. p. 141. tab. 10. fig. 10; Pritch. Infus. p. 184. fig. 99. 



In shallow pools. Weston Bogs, Hants ; Rusthall Common near 

 Tunbridge Wells ; Piltdown Common near Uckfield ; Rackham Com- 

 mon near Pulborough ; Ashdown Forest and Mayfield, Sussex, Mr. 

 Jenner ; Barmouth, Rev. T. Salwey ; Dolgelley and Penzance. 



Fronds rough with minute granules, deeply constricted in the 

 middle, the constriction forming a rounded sinus on each side ; 

 segments obtuse at the sides, about t\\'ice as broad as long, trans- 

 versely oblong. The segments are twisted, and in the front view 

 one of them appears shorter and thicker at one of its sides in 

 consequence of the blending together of two of the angles. The 

 end view is triangular, ^nth concave sides and very obtuse entii'e 

 angles. 



The conic gi'anules, arranged in transverse lines at the angles, 

 are generally veiy minute, but in some Sussex specimens gathered 

 by Mr. Jenner they are large, and on the margin produce a den- 

 tate appearance. 



Stourastrnm tricorne connects the three preceding uith the two 

 following species. It agrees with the former in having rounded 

 entire angles, but in other respects more nearly approaches the 

 latter. It may be known from all states of S. muricatum by the 

 rounded sinuses of its front view. 



Plate XI. fig. 2. S. tricorne : a, front view ; b, end view ; c, empty seg- 

 ment. 



8. S. gracile. Fronds rough ; segments in the front view elongated 

 on each side into a slender process, which is terminated by three 



