484 
Transactions of the Society. 
£ S 17. E. inerme (Ralfs) Lund. III. Th. YII. D. 
18. E. erosum Lund. var. notabile West. I. Ep. III. Bi. VIII. L. 
19. E. pyramidatum West. III. Th. VIII. W. 
20. E. insular e (Wittr.) Roy. VI. N. 
21. E. binale (Turp.) Ehrenb. I. Ep. III. Bi., C., E., M., Mp., 
Pu., Th. IV. Ivs. VI. N. (with zygospores). VII. D., Gp. 
VIII. G., H., HI., K., L., Ii, W. 
Forma minor West. III. Pu. 
Var. elobatum Lund. III. Ew. 
22. E. denticulatum (Kirchn.) Gay. III. Bi., C., E., Ew., Mp., 
Th. IV. Ks. VI. N. VII. D. VIII. L. 
Genus Micrasterias A g. 
1. 31. mucronata (Rahenh.). III. C., Th. 
2. 31. americana (Ehrenb.) Ralfs. III. Mp. 
3. 31. angulosa Hantzsch. III. Th. VI. N. 
4. M. denticulata Breb. III. C., E., Ew., Th. (with zygospores). 
IV. Ks. VII. D. VIII. H. (with zygospores), HI, R., Tm., W. 
5. 31. rotata (Grey.) Ralfs. III. Pu. IV. Ks. VII. D., Gp. 
VIII. L., R., Tm. 
6. 31. Thomasiana Arch. III. C., Th. 
7. 31. radiosa Ralfs. III. Mp. 
8. 31 papillifera (Breb.). III. Th. VII. D. VIII. L. 
9. 31. truncata (Corda) Breb. III. Bi., C., E., Th. VII. D. 
VIII. G., HI, W. 
Var. Bahusiensis Wittr. VI. N. 
10. 31. Jenneri Ralfs. III. Th. VI. N. 
Var. simplex West. VI. N. 
Genus Xanthidium Ehrenb. 
1. X. armatum (Breb.) Rabenh. III. C., E., Th. VII. D. 
VIII. H., R., W. 
2. X. fasciculatum Ehrenb. III. Ew., Mp. VIII. H. 
3. X. cristatum Breb. VI. N. VIII. G., H. 
4. X. antilopseum (Breb.) Kutz. I. Ep. III. Mp., Th. (with zy- 
gospores). VI. N. VII. D. VIII. G., H. 
5. X. Smithii Arch. var. variabile Nordst. III. Dj. (with zygo- 
spores), E., Th. 
6. X. concinnum Arch. ( Arthrodesmus hexagonus Boldt). 
The typical form is rather more deeply constricted than the var. 
Boldt ianum ; there are two small mucros at the apical angles, but only 
one at the lateral angles, this character being well seen in vertical 
view. (PI VI. fig. 15.) 
Long. 9-9*5 ya; lat. s. mucr. 9*5-10*5 ya; lat. isthm. 
2*5-3 ya; crass. 7 ya. III. Pu., Th. 
Var. Boldtianum West ( Arthrodesmus hexagonus Boldt 
forma Boldt). III. Th. 
