EXPLANATION OF THE PLATES. 19 



c, showing the mode of formation of new segments. — Fig. 8. 

 Trigonocystis mucronata : a, front view of different forms 

 of the species ; b, end view ; c, conjugated fronds with the 

 sporangium ; d, state of the sporangium. — Fig. 9. Tri- 

 gonocystis muricata : a, front view ; b, end view ; c, empty 

 frond. — Fig. 10. Trigonocystis mnricata var. rugosa : a, 

 front view; b, end view. — Fig. 11. Trigonocystis tricornis : 

 a, front view ; b, end view ; c, end view of empty frond. — 

 Fig. 12. Trigonocystis aculeata: a, front view; b, end 

 view ; c, end view of variety. 



PLATE LXXXV. 



Fig. 1. Trigonocystis gracilis; a, front view ; b, c, end views. 



— Fig. 2. Trigonocystis bifida : a, a, front views ; b, end 

 view ; c, formation of new fronds. — Fig. 3. Staurastrum 

 paradoxum : a, front view ; b, end view ; c, new segment. 



— Fig. 4. Staurastrum ? tetraceum : a, front view ; b, end 

 view ; c, side view. — Fig. 5. Staurasfrum dilatatum : 

 a, front view ; b, end view. — Fig. 6. Pcntastcrias Jenneri ; 



a, front view ; b, end view ; c, empty segment. — Fig. 7. 

 Pcntasterias margaritaceum : a, front view ; b, b, end views. 



— Fig. 8. Pcntasterias arachne : a, front view ; b, end view. 



— Fig. 9. Arthrodesmus Conner gens : a, front view ; b, end 

 view. — Fig. 10. Arthrodesmus incus : a, front view ; b, end 

 view. — Fig. 11. Arthrodesmus octocornis : a, front view; 



b, end view. 



PLATE LXXXVI. 



Fig. 1. Cosmariummargaritiferum. — Fig. 2. Cosmarium Bo- 

 trytis. — Fig. 3. Cosmarium ornatum. — Fig. 4. Cosmarium 

 cylindricum. — Fig. 5. Cosmarium orbiculatum. — Fig. 6. 

 Cosmarium crenatum. — Fig. 7. Cosmarium Cucurbita. — 

 Figs. 8 and 9. Cosmarium ovale. — Fig. 10. Cosmarium 

 Cucumis. — 'Fig. 11. Cosmarium quadratum. — Fig. 12. 

 Cosmarium quadratum, var. — Fig. 13. Pediastrum Bory- 

 anum. — Fig. 14. Pediastrum angidosum. — Figs. 15 and 16. 

 Pediastrum constrictum. — Fig. 17. Pediastrum tetras. — 

 n 2 



