POTOMAftETOjr. ' 365 



E. B. S. 2685. S. vii. 27. P. euspidatus Sni., F. contpressus 

 Fries. — Ped. 2—4 ini long. Spikea 10 — lo-flowered. Inner 

 edge of fr. rounded; faces a little convex. L. suddenly acumi- 

 nate or apicula,te. — Rivers and lakes. P. ^T E. S. I. 



16. P. aeutifdlius (Link) ; St. flattened, I. linear acuminate 

 with 3 principal and many close parallel intermediate veins occu- 

 pying the whole surface, spiJces ovate about as long as the shoH 

 ped., Sep. rhomboidal, fr. broadly i-obovate compressed inner 

 edge strau/ht mith a tooth near its base keeled, style facial. — 

 JE: B. S. 2609. J?, vii. t. 26.— Ped. very short. Spikes 4^6- 

 flowered. L. gradually acuminate. St3'les hooked, continuing 

 the inner edge of the fruit. — Marsh ditches, rare. P, VI. . E. 



17! P. obtusifoliii^ • (Koch) ; st. slightly compressed vA\h 

 rounded edges, /. linear ^-hieined, irpikes ovate dense continuous 

 about as Iraig as the short ped., sep. rhomboidal, fr. obovate 

 keeled. — B. rii. t. 25. P. gramineus Sm., M B. 2253. — St. 

 sleudea:, much branched. ~ Peduncles very short. L. rounded 

 off to a slight point ,^f the end, with oblong network near the 

 midrib, wanting the fine parallel veins of the two preceding 

 species. — Pond3.and ditches, rare. P. Vl. VII. E. S. 1. 



18. P. eompres'siis (L.);,st. slightly- compressed, I. litiear 5- 

 veined suddenly apiculate, spikes short lax J. or |- shorter 

 than the cdnipressed clavate ped., sep. transversely oval, fr. ob- 

 liquely ovate bluntly' keeled.— jB. JS. 418. iJ. vii. 24, not PHes, 

 nor Koch. — ^Lateral veins nearer together and nearer tp the 

 margin of the 1. than to the'midrib (rarely some 1. are 3-veined), 



no intermediate veins Like Ko. 15 rather than 17. — Ditches. 



P. %TVIL ' ' ' E. S. L 



19. P. pusUlm (L.); st. subterete, I. linear 8-veined, spikes 

 short rather lax 5 or f .shprter than the slender ped., sep. 

 roundish-reniform, fr. obliquely ovate bluntly, keeled. — JE. B. 

 215. P. vii. 22. — St. slender. L. narrow, rather acute, without 

 intermediate parallel veins, the lateral veins equidistant between 

 the midrib and margin. Ped. scarcely compressed, not thickened. 

 — [P. rutHus. (Wolfe., Fries) has 3-veined attenuate-cuspidate 

 1., semiterete st., and oblong-elliptic fr. without a keel^^P. gra- 

 cilis of Mait. ed. 4. seeinsto be P. pusillus.'] — Ponds and ditches. 

 P. VL ' E. S. 1. 



20. P. trichoides (Cham.) ; st. subterete, /. subsetaceous 1- 

 veined finely pointed, spikes short lax long-stalked, fr. semicir- 

 cular compressed obscurely keeled, straight inner edge ufith a 

 tooth near its base. — P. vii. 21. — St. very slender, a little thick- 

 ened belovr the joinings ; branches fasciculate. ' L. not trans- 

 versely v6ined. Flor£d' stip. large. Ped. not thickened. Sep. 



