ARTHRODESMUS. 357 



1. AKTHRODESMUS CONVERGENS JEhr. 

 Plate LXXXY. Fig. 9. 



Char. Segments broader than long, somewhat elliptic, elon- 

 gated at each side into an incurved spine. End vie\v 

 compressed, with a spine at each extremity. 



Arthrodesmus convergens Ehr., Infus. p. 152. t. 10. fig. 18. 

 Staurastrum convergens Menegh., Synops. Desmid 

 p. 228. ; Ralfs, in Annals, vol. xv. p. 158. pi. xii. fig. 1. ; 

 Bailey, Amer. Bacil. pi. i. fig. 11.; Jenner, in loc. cit. 

 p. 194. 



Hal. Brambletye, near East Grinstead ; Rackham Com- 

 mon, near Pulborough, Sussex ; and Rusthall Common,, 

 near Tunbridge Wells : Mr. Jenner. Dolgelly and 

 Penzance : Mr. Ralfs. Cheshunt : A. H. H. 



The incurved mucrones will at once serve to distinguish 

 this species. 



2. ARTHRODESMUS INCUS Hass. 

 Plate LXXXV. Fig. 10. 



Char. Segments externally lunate, with a mucro at each 

 angle. End view elliptic, mucronated at each extremity. 

 Euastrum Bailey, Amer. Bacil. pi. i. fig. 12. ? Staurastrum 

 Incus Meneghini, Synops. Desmid. p. 228. ; Ralfs, in 

 Annals, vol. xv. p. 159. pi. xii. fig. 2. ; Jenner, p. 194. 



Hal. Weston Bogs, near Southampton; Rackham Com- 

 mon, near Pulborough, Sussex : Mr. Jenner. Dolgelly 

 and Penzance : Mr. Ralfs. 



The mucro in this species is turned outwards : in the front 

 view the segments resemble those of Trigonocystis mucro- 

 nata, but the end view is very different. 



3. ARTHRODESMUS OCTOCORNIS JEhr. 

 Plate LXXXV. Fig. 11. 



Char. Fronds compressed. Segments broader than long, 



A A 3 



