126 BRITISH DESMIDIF.^. 



Sfaurasfrum orhiculare may be recognized by its smooth frond, angles 

 broadly rounded and destitute of processes, and its orbicular form in a front 

 view. 



Sporangia, gathered at Dolgelley and Penzance, are orbicular, with subulate 

 spines. The conjugating fronds are smaller than those in the ordinary state. 



Length of frond t-qVt °^ ^^ mch ; breadth y-poT 5 breadth at consti'iction 

 ■g-^Vr ; cliameter of sporangium -^-^ ; length of spine ^ ^^3 g . 



Tab. XXI. fig. 5. a, c, d, h. front vieAV ; b,f, i. end view; e. transverse 

 view ; g. sporangium. 



9. S, tumidum (Breb.) ; segments smooth, elliptic or suborbicular ; 

 end view bluntly triangular, each angle terminated by a nipple-like 

 projection. 



Binatella tumida, Brebisson, Alg. Fal. p. GQ (1835). 



Staurastruyn orhiculare, Meneghini, Synop. Destnid. in Linncea 1840, p. 225. 



Staiirastrum tumidum, Brebisson, in lit. cum icone (1846). 



Piltdown Common, Sussex, Mr. Jenner. Dolgelley and Penzance, /. R. 



Falaise, Brebisson. 



Frond large and distinctly visible to the naked eye, smooth, deeply con- 

 stricted at the middle, having a distinct gelatinous covering, which is often 

 marked with close radiating striee ; segments elliptic or suborbicular. The 

 end view is triangular or quadrangular, the sides are convex, the angles 

 rounded, and each terminated by a nipple-like process ; some of these pro- 

 jections are visible in the front view. In both views the margin of the frond 

 appears striated. The empty frond is minutely punctate. 



Length of frond ^^^ of an inch ; breadth -^\-^ ; breadth at constriction j-g-Q . 



Tab. XXI. fig. 6. a. front view; b. end view of triangular form ; c. end 

 view of quadrangular variety magnified only 200 times ; d. transverse view. 



*** Frond with simple spines, hairs, or {rarely) acute granules ; 

 angles, in end view, broadly rounded and entire. 



10. S.muricatum (Breb.) ; segments semiorbicular, rough with conic 

 granules ; end view triangular, with convex sides and broadly 

 rounded angles. 



Binatella muricata, Brebisson, Alg. Fal. p. && (1835). 



Desmidium apiculosum, Ehrenberg, In/us. p. 142 (1838). Pritchard, Infus. 



p. 184. 

 Staurastrum muricatum, Brebisson, Meneghini, Synop. Desmid. in Linncea 



1840, p. 22G. 

 Xanthidium deltoideum, Corda, Ohseri\ Microscojvques sur les Animalcides 



de Carlsbad, p. 29. t. 5. f. 38, 39 (1840). 

 Staurastrum muricatum /3, Ralfs, Annals of Nat. Hist. v. 15. p. 154. t. 11. 



f. 1. ^, e. (1845) ; Trans, of Bot. Soc. of Edinburgh, v. 2. p. 141. t. 14. 

 Phycastrum apiculosum, Kiitzing, Phy. Germ. p. 137^ (1845). 



