324 
POTAMEjE. 
cording to Koch, the P. acuminatus Schum. — Common in deepish 
water. P. VI. 
8. P. longif alius (Gay) ; I. pellucid elongate-lanceolate narrowed 
below entire apiculate, stip. winged, nuts , peduncles very long 
swelling upwards, spikes with few subverticillate distant flowers. 
— E. B. S. 2847. — St. long, slender. L. distant, quite entire, 
nearly sessile with very short stalks. Stipules green, lanceolate, 
with 2 narrow wings on the back. Peduncles 6—8 in. long and 
much thicker than the stem, suddenly contracting at the spike 
which is about an inch long and has the fl. rather more decidedly 
whorled than they are represented in E. B. S. The nuts have 
not been described. — Deep water. Lough Corrib, Galway ; 
and near the larger island in Rydal Water, Westmoreland. Mr. J. 
Ball. P. VIII. E. I. 
9. P. pralongus (Wulf.) ; I. pellucid elongate-oblong half- 
clasping obtuse and hooded at the end entire, stip. not winged, nuts 
rounded on the back when fresh heeled when dry, peduncles very 
long equal, spikes many-flowered. — E. B. S. 2858. — St. long, 
growing in deep water and forming dense masses of foliage just 
below the surface. Peduncles 6 — 12 in. long. Spikes 1 — 2 in. 
long. — Rivers and ditches, rare. P. VI. 
10. P. perfoliatus (L.) ; st. round, I. pellucid cordate-ovate 
clasping serrulate plane, nuts rounded on the back when fresh, 
keeled when dry, peduncles equal. — E. B. 168. — St. long, slightly 
branched. Peduncles rather thick and short. Spikes short. — ■ 
Lakes and streams. P. VII. 
11. P. crispus (L.) ; st. compressed, I. pellucid linear-oblong 
obtuse sessile serrulate wavy, nuts with long beaks keeled on the 
back when dry, peduncles equal.— £.5.1012. — St. much branched. 
Peduncles elongated. Spikes few-flowered. Beak as long as the 
nut. L. usually crisped at the edges, occasionally plane when 
it is P. serratum Huds. — Ditches and streams. P. VI. 
*** L. all submersed, alternate, linear; stipules free. 
12. P. zosterafolius (Schum.) ; st. flattened, I. linear-acumi- 
nate with, 3 principal ribs and numerous close parallel intermediate 
nerves occupying the whole surface, spikes cylindrical upon long 
peduncles, nuts obovate keeled, style terminal. — E. B. S. 2685. 
P. cuspidatus Sm., P. compressus " L.," Fries, Koch. — Peduncles 
2 — 4 in. long. Spikes 10 — 15-flowered. L. suddenly acuminate 
or apiculate. — Rivers and lakes. P. VI. E. S. 
13. P. acutifolius (Link) ; st. flattened, I. linear-acuminate with 
3 principal ribs and numerous close parallel intermediate veins oc- 
cupying the whole surface, spikes ovate about as long as the short 
peduncle, nuts reniform acutely keeled, style facial. — E. B. S. 
2609. — Peduncles very short. Spikes 4 — 6-flowered. L. gradu- 
