Stomata present. 



Mo.st of the spines short, broad, usually retuse, leaves 25 or 

 less. 8a. echinospora Braunii. 



Like No. 8a, but leaves 25-70, and more densely stomatose. 

 8b. echinospora robusta. 



Spines long and slender, sharp or forked, leaves stiffly erect. 



Sc. echinospora Boottii. 



Spines often mixed with short crests, otherwise as in No. 8a, 

 spores larger, leaves long and slender. 



8d. echinospora muricata. 



Group 3. 



Plants growing in ditches or near the borders of ponds at higher 

 levels than the preceding, emersed during the greater part of the 

 summer. Stomata many, and bast-bundles (in our species) four. 



Palustres. 

 Spores smaller (450 ^ or less). 



Closely set with irregular, thick, rough, anastamosing 



ridges. 9. Eatoni. 



Densely covered with short, truncate columns. 10. Gravesii 



Spores larger (averaging over 550 ft) with irregular, usually scat- 

 tered, variously anastamosing crests, ii. Dodgei. 



Spores medium ( averaging about 450 fi } , regularly honeycomb- 

 reticulated. 

 Plants larger, with stouter leaves, and four bast-bundles, 



12. Engehnanni. 



Plants weaker, leaves 15 or less, often without bast-bundles. 

 I2a. Engehnanni gracilis. 



I. I. LACUSTRIS L. 



Quite common in clear waters in northern Europe. Variously 

 reported from North America, but most reports have proven erro- 

 neous. The nearest approach to it I have yet met, was collected 

 by Coville in Kennebago lake, Maine, in 1895. I have referred his 

 plants doubtfully to Tuckermani borealis. 



2. I. heterospora n. sp. 



Trunk bi-lobed, leaves 50-75, 5-8cm. long, very stiffly erect, 

 nearly 2mm. in diameter, tapering to a sharp point, wanting stomata 

 or bast : velum J/j-% indusiate : sporangium spotted, often thickly 

 so, with dark cells ; macrospores normally 540-675 //, but occasion- 

 ally i loo or even 1134 n, densely covered with thick, jagged, con- 

 voluted crests, often honeycomb-reticulated below ; microspores 

 30.8-39.6 ft, averaging 35x27 p, dark brown, papillose. 



