134 BRITISH DESMIDIE^. 



in transverse lines. Meneghini describes the rays as varying in number from 

 three to five. 



Staurastnim diJatatum differs from S. alternans in not being twisted ; its 

 rays also (in an end view) are more truncate. 



Length of frond ytot ^^ ^^ ^^^^^ 5 breadth xrrr '■> breadth at constriction 



1 



TTsi' 



Tab. XXI. fig. 8. a. front Aaew of frond ; b. end \'iew ; c. transverse view. 



23. S. margariiaceum (Ehr.) ; segments rough tapering at the con- 

 striction, and having short lateral processes ; end view with five or 

 more short, narrow, obtuse rays. 



Pentasterias margaritacea, Ehr. Infus. p. 144. t. 10. f. 15 (1838). Pritch. 



Infus. p. 185. f. 104. 

 Stmirastrum margaritaceum, Menegh. Synoji.Desmid. mLinncea 1840, p. 227. 



Ralfs, Jyinals of Nat. Hist. v. 15, p. 157. t. 11. f. 7 ; Trans. ofBot. Soc. 



of Edinburgh, v. 2. p. 144. t. 14. 

 Phycastrum margaritaceum, Kiitzing, Phycologia Ger-m. p. 138 (1845). 

 Goniocystis {Pentasterias) margaritacea, Hassall, Brit. Freshwater Algee, 



p. 356 (1845). 



Dolgelley, J. R. Ashdown Forest, Sussex, 3Ir. Jenner. Stoke-Hill near 

 Wells, Mr. Thwaites. Aberdeenshire, Dr. Dickie and Mr. P. Grant. Am- 

 bleside, Mr. Sidebotham. 



Germany, Ehrenberg. Falaise, Brebisson. West Point, New York, Bailey. 



Frond rough with minute pearly granules ; in the front view the segments 

 are convex at the ends and slightly attenuated at their junction, and on each 

 side there is a short, linear, obtuse and entire process, which is generally 

 somewhat incurved ; occasionally these processes are mere conical projections, 

 but they may always be perceived. The end \-iew has from five to seven short, 

 narrow, obtuse, marginal rays. 



M. de Brebisson unites S. margaritaceum to S. dilatatum, but they appear 

 to me to be distinct. In the front view of the latter the segments do not taper 

 at their junction, are broader than long, and have no processes visible at the 

 sides ; in all which respects it differs from S. margaritaceum. 



Length of frond -j-jVb" °^ ^"^ ^"^^ '■> breadth, including processes, yoVo 5 

 breadth, excluding processes, ^stt 5 breadth at constriction -gaVg-. 



Tab. XXI. fig. 9. a, b. front A-iews ; c, d, e. end views. 



24. S. tricorne (Breb.) ; frond rough with puncta-like granules ; seg- 

 ments tapering at each side into a short, blunt, mostly entire pro- 

 cess ; end view with three or four blunt angles. 



/3. Processes terminated by minute spines. 



Binatella tricotmis, Brebisson, Jig. Fal. p. 57. t. 8 (1835). 

 Desmidlum hexaceros, Ehr. Infus. ]). 141. t. 10. f. 10 (1838). 

 Staurastrum tricorne, Meneghhii, Synop. Desmid. in Linncpa 1840, p. 225. 

 Brebisson, in lit. cu7n icone. 



