Freshwater Algoe of S. of England. By W. &' G. S. West. 479 
I. Ep. III. Bi., C., E, Ew, Pu., Tb. IV. Ks. VII. D. VIII. 
G, H., ID, T, W. 
Var. constrictum West. VI. N. 
7. P. interruptum Breb. III. Pu. 
8. P. Nagelii Breb. III. Th. VI. N. 
Long. 115 /x; lat. 25 /x. 
9. P. libellula (Focke) Nordst. (P. closterioides Ralfs). III. C., 
Tb, Wo. VII. D. VIII. H. 
Forma interrupta West. III. C. 
10. P. Navicula Breb. I. Ep. HI. E, Ew, Fb, Tb. IV. Ks. 
VI. N. VII. B. VIII. H, L. 
11. P. rufescens Cleve (P. rufopellitum Boy). III. Bi. 
12. P. curium Breb. III. Pu., Th VII. Gp. 
Forma major Wille. III. Mp. 
Long. 59 fi ; lat. 30-32 /x. 
I 13. P. suboctangulare West. VI. N. (with zygospores). 
14. P. subtile sp. n. (PI. VI. figs. 8, 9.) 
P. ruinutissimum, p*ene lj-plo longius quam latum, 
ellipticum, apicibus subtruncatis, medio cum sutura mediana 
delicatissima (levissime constrictum) ; a vertice visum exacte 
circulare ; membrana achroa, delicatissime et indistincte 
punctulata, punctulis sparsis circiter 12 in semicellula una- 
quaque. 
Long. 14-15 fi ; lat. 10-11 /x. III. Tb. 
This minute species was in abundance and was perfectly constant 
in its characters. The widest part of the cell is always in the middle , 
and the apices are always flattened. 
It can be compared with Disphindium spar sipun datum Schmidle 
(in (Esterr. botan. Zeitschrift, 1895, No. 7, p. 14 (sep.) t. xv. f. 1-0), 
from the unconstricted form of which it differs in the form of its cells, 
its much more delicate punctulations, and its circular vertical view. 
15. P. truncatum Breb. VII. D. VIII. T, W. 
1 6. P. polymorphum Perty. III. C. VIII. P. 
17. P. inconspicaum West. III. Pu. IV. Ks. 
18. P. cruciferum (Be Bary) Wittr. I. Ep. III. Wi. 
19. P. cucurbitinum Bissett. I. Ep. III. Th. 
20. P. minutum (Ralfs.) Cleve. III. C, Pu, Th. VI. N. 
VII. B. VIII. R, W. 
Genus Boy a West & G. S. West. 
1. P. obtusa (Breb.) West & G. S. West var. montana West & 
G. S. West. I. Ep. III. Ew. 
Genus Closterium Nitzsch. 
1. C. abruptum West, III. Pu, Wi. VI. N. VII. B. 
2. C. didymotocum Corda. III. C, Th. VII. B. VIII. H, P. 
