140 BRITISH DESMIDIE^. 



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 

 roiuided, but in /3. 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 \iew, in which the sides are nearly straight, has the angles in 

 a. rounded, but in j3. 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 -S. muricatum. S . punctulatmn is smaller, and its granules are more 

 like pmicta than spines. In S. rugulosum the segments in the front view are 

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

 to the angles. 



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

 diameter of sporangium -g-i^ ; length of spmes 3-5x0 • 



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



Tab, XXIII. fig. 12. a. sporangium ; b. front view of variety (^ ; c. end 

 view. 



tt End 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, /. R. 

 Falaise, Bi-ebisson. 



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

 gular notches ; segments having on each side a spine forked like the tail of a 

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

 tipped by a spine. 



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



Length of frond 9^^ of an inch ; breadth gig ; breadth at constriction 2X03^ > 

 length of spine xwt%- 



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. B. 



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

 diff"ers but little 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 



