140 BRITISH DESMIDIEvE. 



margin is flattened, and its spines are usually more evident than the rest, and 

 are also in general slightly forked. In a. the lateral margins are broadly 

 rounded, but hi jo. they extend into a process about as long as broad and 

 tipped with a few acute spines, which are larger than those on the segment 

 itself. The end view, in which the sides are nearly straight, has the angles in 

 a. rounded, but in (3. terminated by short rays. 



The sporangia, which I have gathered at Penzance, Are orbicular, and their 

 spines are twice branched at the apex. 



The form of the segments distinguishes Staurastrum asperum from all 

 states of 5'. mvricatum. S . punctulatum is smaller, and its granules are more 

 like puncta than spines. In >S^. rugulosum the segments in the front view are 

 elliptic, not tapering at the junction, and its spine-like granules are confined 

 to the angles. 



Length of frond -j^-g of an inch ; breadth ^^r ; breadth at constriction ^^^ ; 

 diameter of sporangium yi-g ; length of spmes a-gVo • 



Tab. XXII. fig. 6. a. front view ; b. end view. 



Tab. XXIII. fig. 12, a. sporangium ; h. front \'iew of variety /3 ; c. end 

 view. 



tt ^nd view acutely triangular ; segments, in the front view, with a 

 forked spine on each side, otherwise smooth, 



32. S. Avicula (Breb.) ; segments with a forked spine on each side ; 

 each angle, in end view, terminated by a mucro-like spine. 



Staurastrum Avicula, Brebisson, in lit. cum icone (1846). 

 Penzance, very rare, J. R. 

 Falaise, Brebisson. 



Frond very minute, scarcely rough, the constriction producing wide trian- 

 gular notches ; segments ha\'ing on each side a spine forked like the tail of a 

 swallow. End view with three slightly mflated angles or lobes, which are 

 tipped by a spine. 



The forked lateral spines of the front view mark the species. 



Length of frond g^iy of an inch ; breadth gig- ; breadth at constriction 2X0^ 5 

 length of spine xfts-- 



Tab. XXIII. fig. 11. a. front view; b. end view. 



ttt Lobes in end view broad, emarginate or bipartite. 



33. S. enorme ; frond irregular or quadrate, spinous ; end view 



three- or four-lobed ; lobes broad, more or less emarginate or bifid, 

 and terminated by spines which are either simple or branched. 



Dolgelley, J. R. 



Frond very irregular and variable in form. Sometimes the front view 

 differs but httle from the end one, usually however there is a slight con- 

 striction or sinus at the junction of the segments, but I have never observed 



