BRITISH DESMIDIE^. 133 



I have gathered the sporangia at Penzance ; they are orbicular and fur- 

 nished with spines forked at the apex. 



Length of frond ^^^3;^ of an inch ; breadth ^0^ ; breadth at constriction 



3 2 5 • 

 Tab. XXI. fig. 7. a. front view ; h. end view ; c. transverse view. 



21. 8, punctulatum (Breb.) ; segments rough with puncta-like gra- 

 nules, elliptic, equal ; end view with broadly rounded angles and 

 slightly concave sides. 



iStaurastrum punctulatum, Brebisson, in lit cum icone (1846). 

 Sussex, Mr. Jenner. Dolgelley, J. B. 

 Falaise, Brebisson. 



Frond larger than that of Staurastrum alternans, rough with minute pearly 

 granules which appear like puncta ; segments tmce as broad as long, elliptic ; 

 end view triangular with very blunt angles. 



Staurastrum punctulatum may be distinguished from S. alternans by its 

 equal and more turgid segments in the front view, and in an end one by its less 

 concave sides. S. rugulosum agrees with it in size and partly in form, but in 

 that species the pearly granules are larger and fewer, and at the angles appear 

 like little spines. 



Length of frond y^ of an inch ; breadth g-lr ' breadth at constriction j-oVo • 



Tab. XXII. fig. 1. a. front view; b. end view of empty frond; c. dividing- 

 fronds. 



22. S. dilatatum (Ehr.) ; segments rough, fusiform, equal ; end view 

 with four short, broad, truncate and entire rays. 



Staurastrum dilatatum, Ehr. Infus. p. 143. t. 10. f. 13 (1838). Menegh. 



Si/nop. Desmid. in Linncea 1840, p. 156. Pritch. Infus. p. 184. Ralfs, 



Amials of Nat. Hist. v. 15. p. 143. t. 11. f. 5 ; Tratis. of Bat. Soc. of 



Edinburgh, v. 2. p. 143. t. 14. 

 Phycastrum dilatatum, Kiitzing, PJujc. Germ. p. 138 (1845). 

 Goniocystis {Staui'astru7n) dilatatum, liassall, Brit. Freshwater Algce, p. 353 



(1845). 



Dolgelley and Penzance, J. R. Rusthall Common near Tunbridge "Wells, 

 and Rackham near Pulborough, Sussex, Mr. Jenner. Yate near Bristol, 

 Mr. Broome. Ambleside, Mr. Sidebotham. 



Germany, Ehrenberg, Kiitzing. Falaise, Brebisson. West Point, New 

 York, Bailey. '- 



Frond very minute, rough with puncta-like pearly granules, deeply con- 

 stricted at the middle, the sinuses rounded ; segments fusiform, two or three 

 times broader than long, equal, obtuse at the sides, and not elongated into 

 processes. In the end view, which is quadrangular, the sides are concave, and 

 the angles form short, broad, truncate rays, on which the granules are arranged 



k2 



