/» ARCHER AND DIXON, ON DESMIDIACE.E. 



view tri-radiate, haying projecting from each side at equal 

 intervals the parallel pair of spines unaccompanied by others ; 

 processes terminating each angle in this view, straight, elon- 

 gate ; endrochrome restricted to the centre, triradiate. 



Length of frond, -fa of an inch; breadth, ^ ff to ff i^j 

 breadth of constriction -^tff- 



Plate VII. Fig. 1, front view ; fig. 2, end view. 



This form appears to me very distinct from any described. 

 The presence of the conspicuous pair of acute spines pro- 

 jecting from each margin at end view distinguishes it from 

 all but Staurastrum vestitum, but in that species the spines, 

 which are apparent only in the end view, are emarginate at 

 the ends, and often accompanied by others of considerable 

 size ; and indeed, even the smaller are themselves often 

 emarginate ; moreover, in the front view it differs by its 

 converging process. It is also considerably smaller than 

 Staurastrum vestitum, being not more than half its width, 

 which diameter in that species greatly exceeds its length. 

 The converging processes in front view are somewhat like 

 those of S. cyrtocerum ; but in that species there are no spines 

 at the ends of the fronds, and the processes in end view are 

 not so much prolonged, and are curved in place of straight. 

 The presence of the marginal spines in end view, and the 

 incurved, not divergent, or parallel processes in the front view, 

 distinguish this from S. paradoxum, S. gracile, and S. poly- 

 morphum. 



Staurastrum nitidum (sp. nov.) 



Specific characters : Frond rough at the ends, with a series 

 of papilla-like granules ; segments broadly elliptic ; end view 

 triangular ; sides convex, with a submarginal series of 

 papillae ; angles not inflated, mucronate. 



Locality : Pools near " Sugar-loaf;" rare. 



General description : Fronds about as broad as long; seg- 

 ments broadly elliptic, inner margin somewhat more turgid 

 than the outer, sub-mammillatc at each side, terminated by a 

 mucro, and on the outer margin rough with a scries of 

 minute papilhe, otherwise smooth; constriction forming a 

 broad notch, with an acute angle; end view triangular, sides 

 convex, with an inwardly curved sub-marginal series of 

 papillae, their summits directed somewhat towards the angles ; 

 angles not inflated, the last papilla forming a terminal mucro ; 

 endochrome in both views disposed in a radiate manner; 

 gelatinous investment evident. 



