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. Staurastrum dilatatum : 



a, front view ; b, end view. Fig. 6. Pentasterias Jenneri ; 

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

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



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



Fig. 9. Arthrodesmus convergens : 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. Cosmarium margaritiferum. Fig. 2. Cosmarium Bo- 

 try tis. 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 angulosum. Figs. 15 and 16. 

 Pediastrum constrictum. Fig. 17. Pediastrum tetras. 



B 2 



