1922] 



PFEIFFER — MONOGRAPH OF THE ISOETACEAE 181 



water, 11 August, 1902, Shull 201 (Gray Herb.) ; so. margin 

 Four Mile Run, 19 November, 1895, Coville 123 (U. S. Nat. 

 Herb.) ; tide beach in mud and gravel, mouth of Four Mile 

 Run between Washington and Alexandria, 5 August, 1898, 

 Steele (Mo. Bot. Gard. Herb, and IT. S. Nat. Herb.) ; Four 

 Mile Run, 4 mi. south of Washington,, D. C., 22 August, 

 1902, Shull 252 (Mo. Bot. Gard. Herb, and U. S. Nat. 

 Herb.); Four Mile Run, near Alexandria, abundant be- 

 tween tidal limits, 12 July, 1905, Ivar Tidestrom (Gray 

 Herb.) ; Hunting Creek, Alexandria, 13 August, 1910, Dowell 

 6455 (U. S. Nat. Herb.). 



48. I. riparia Engelm. A. Br. in Flora (Regensb. Bot. Zeit.) 

 29: 178. 1846; Am. Jour. Arts and Sci. 3: 52. 1847; Baker, 

 Jour. Bot. 18: 69. 1880; Motel. & Vendr. Aetes Soc. Linn. Bord. 

 36: 368. 1883; Engelm. Trans. St. Louis Acad. Sci. 4: 382. 1884; 

 Macoun, Cat. Canad. PI. pt. 4: 293. 1888; Eaton in Gray, Man- 

 ual, ed. 7, 60. 1908; Maxon in Britton and Brown, 111. FL, ed. 

 2,52. 1913. 



Calamaria riparia Kuntze, Rev. Gen. PI. 2 : 828. 1891-93. 



Corm 2-lobed; leaves 10-30, 9-30 cm. long, rather rigid, more 

 slender than /. lacustris, deep green in color, with membranace- 

 ous margins but briefly extended; stomata numerous; periph- 

 eral strands lacking; ligule elongated, with narrow tip, ovate 



at base; sporangia spotted with brown cells, oblong, 4-7 mm. 



long, with narrow velum (covering sporangia 1/4-1/3) ; mega- 

 spores white, 440-660 \\ in diameter, marked with conspicuous 

 jagged crests, often with isolated peaks standing out sharply, 

 sometimes anastomosing slightly; microspores cream-colored in 

 mass, 25-33 \\ long, tuberculate. 



Distribution : southern Canada, New England, south to Dela- 

 ware and Pennsylvania. 



Specimens examined: 

 Canada: Crow River, northwest of Belleville, Hastings Co., 18 



July, 1864, Macoun (Mo. Bot. Gard. Herb, and N. Y. Bot. 

 Gard. Herb.). 



Maine: Cornish, 1859, Chickering 7 (Mo. Bot. Gard. Herb.). 



Connecticut: Lantern Hill Pond, North Stonington, 23 July, 



1901, Graves & Bissell (Mo. Bot. Gard. Herb.) ; Lantern 

 Hill Pond, North Stonington, 23 July, 1901, Bissell (Gray 



