BRITISH DESMIDIEiS. 13/ 



Goniocystis (Pentasterias) arachnis, Hassall, Bi-it. Freshwater Ala. i3. 355 

 (1845). 



Dolgclley, very rare, J. R. Aberdeen, Mr. P. Grant. 

 Falaise, Brebisson. 



Frond minute, deeply constricted at the middle ; segments about as long 

 as broad, having on each side an elongated process, which is hyaline and 

 incurved, and on account of its minute granules appears transversely striated. 

 \\lien the frond is vieAved obliquely, so that three or more of the long curved 

 processes are seen at once, its resemblance to an insect is considerable. The 

 end view is circular with five slender rays. 



This plant is remarkable for its slender processes, which will easily 

 distinguish it from Staurastrum margaritaceum. It cannot be a five-rayed 

 variety of S. gracile or S. pohjmorphum, for its rays are longer, more slender, 

 remarkably incurved and also entire at the extremity. 



Length of frond ^^^^ of an inch ; breadth, excluding processes, -goVo '■> 

 including processes, ^4t '■> l^iigth of process ysW '■> breadth at constriction 



2 7 32* 



Tab. XXIII. fiff. 6. a. front A-iew ; h. end A-iew. 



28. /S. tetracerum (Kiitzing) ; frond rough ; front view with four 

 slender diverging processes w^hich are entire at the apex ; end view 

 compressed, with a process at each extremity. 



Micrasterias tetracera, Kiitzing, Synopsis Diatom, in Linncea 1833, p. 602. 



f. 83, 84. 

 Micrasterias tricera, Kiitzing, /. c. p. 602. f. 85. 

 Staurastrum paradoxum, Ehr. Infus. p. 143. t. 10. f. 14 (1838). Pritch. 



Infus. p. 185. f. 102, 103. 

 Staurastrimi tetracerum, Ralfs, AnnaJs of Nat. Hist. v. 15. p. 150. t. 10. 



f. 1 (1845) ; Trans, of Bot. Soc. of Edinburgh, v. 2. p. 137. t. 13. 

 Goniocystis {Staurastrum 1) tetracerum, Hassall, Brit. Freshwater Alg. p. 354 



(1845). 



Dolgelley and Penzance, J. R. Yate near Bristol, Mr. Broome. Aber- 

 deenshire, Mr. P. Grant. Ambleside, 3Ir. Sidebotham. Midhurst, Battle, 

 and Cross-in-Hand, Sussex, Mr. Jenner. 



Germany, Kiitzing, Ehrenberg. Falaise, Brebisson. United States, Bailey. 



Frond very muiute ; front view nearly square, the angles elongated into 

 straight, slender processes which diverge from each other ; frequently how- 

 ever a segment may be so twisted, that one of its processes is situated behind 

 its companion, and is not seen vuiless carefully looked for ; in this case the 

 frond seems to have only three processes in a front Anew. The end view is 

 much compressed and terminated both ways by an elongated process. The 

 frond is rough with minute puncta-like granules, which form transverse lines 

 on the processes and give them a jointed appearance. The colouring matter 

 is very pale. 



