GONIOCYSTIS. 355 



Hob. Dolgelly and Penzance : Mr. Ralfs. 



This Staurastrum is to be distinguished from the previous 

 species by the trifid extremities of the rays. 



4. STAURASTRUM ? BIFIDUM Ralfs. 

 Plate LXXXV. Fig. 2. 



Char. Frond smooth) but little constricted in the centre, truncate 

 laterally. Rays trifid. End view triradiate. 



Desmidium bifidum Ehr., Die Infus. p. 141. t 10. f. 11.: 



Ralfs, 1. c. p. 151. pi. x. fig. 3. 

 Hob. Dolgelly and Penzance : Mr. Ralfs. 



The smoothness of the frond will always distinguish this 

 from the previous species. It should probably be referred to 

 Trigonocystis . 



Section iii. PENTASTERIAS Ehr. 



Char. Frond in front view without diverging processes. End 

 view circular, with usually Jive rays. 



Derivation. From TTSVTS, five, and avrspias, starred. 



1. PENTASTERIAS ARACHNIS Hass. 

 Plate LXXXV. Fig. 8. 



Char. Frond rough, deeply constricted in the centre. Seg- 

 ments about as long as broad, suborbicular, with elongated 

 slender hyaline and incurved processes. End view five- 

 rayed. 



Staurastrum Arachne Ralfs, in Annals, vol. xv. p. 157. 

 pi. xi. fig. 6. 



Hob. Boggy pool near Dolgelly, very rare : Mr. Ralfs. 



" This plant is remarkable for its slender processes which 

 will easily distinguish it from St. margaritaceum. It cannot 

 be a five-rayed variety of St. gracile, for the rays are longer, 

 more slender, remarkably incurved, and also entire at the 

 extremity." - Ralfs. 



AA 2 



