144 BRITISH DESMlDlEzE. 



Length of frond -^^ of an inch ; breadth -3^ ; breadth at constriction 

 i._ 



3 2 5* 



Tab. XXIII. fig. I.e. front view ; b, c. end views with endochrome ; d. end 

 view of empty frond ; e. transverse view. 



12. DIDYMOCLADON, n. g. 



Frond simple, constricted at the middle, angular, each angle having two 

 processes, one lateral, and in front view nearly parallel to the ad- 

 jacent one of the other segment, the other superior and divergent. 



The frond is simple, constricted at the middle ; segments angular, 

 as shown by the end view, each angle furnished with two elongated 

 processes, the inferior lateral and nearly parallel to the similar one 

 of the other segment, but the superior directed obliquely outwards 

 and divergent. 



This genus is closely allied to Staurastrum, but has one remark- 

 able differential character. Each angle of the segments gives rise to 

 two processes, one beneath the other, whereas in Staurastrum the 

 process, when present, is solitary from each angle. 



D.furcigerus, Breb. 



a. End view triangular. 



/3. End view quadrangular. 



Staurastrum furcigerum, Breb., Meneghini, Synop. Desmid. in Linncea 1840, 



p. 226; in lit. cum icone. 

 Phycastrnmfurcigo'um, Kiitzing, Phy. Germ. p. 138 (1845). 



Dolgelley, /. R. Brookhouse Moss near Congleton, Cheshire ; and near 

 Ambleside, Mr. Sidehotham. Rochdale, Mr. Coates. Brightling near 

 Burwash, Sussex ; and Weston Bogs near Southampton, Mr. Jenner. 



Falaise, Brebisson. Germany, Kiitzing. 



Frond comparatively large, rough with pearly granules, which being 

 arranged on the processes in transverse lines, produce a crenate appearance 

 on their margins. In the front view the processes are elongated, stout, 

 tapering, bifid at the apex. The lateral processes of the one segment are 

 usually parallel to those of the other ; in Rochdale specimens however they 

 are slightly curved outwards. The end view is triangular or quadrangular, 

 and the elongated angles appear either acute and simple, or bifid, according 

 as one or two forks of the processes may be visible. 



Length of frond, including processes, -3^ of an inch ; length, excluding 

 processes, -g-iy ; breadth, including processes, -^\j ; breadth, excluding pro- 

 cesses, g^i-j ; breadth at constriction ^ /g g . 



Tab. XXXIII. fig. 12. a, b. front views; c. end view of a ; d. transverse 

 view of /3. 



