roTAME.i:. 
325 
allv acuminate. Styles a continuation of the straight inner edge 
of the nuts. — Marsh ditches in Sussex. P. VI. E. 
14. P. gramineus (L. ?) ; st. slightly compressed with rounded 
edges, I. linear 3-nerved, spikes ovate dense continuous about as 
long as the short peduncle, nut obovate keeled. — E. B. 2253. 
P. obtusifolius M. and K. — St. slender, much branched. Pe- 
duncles very short. L. rounded off to a slight point at the end, 
with a few oblong reticulations next the midrib but wanting the 
numerous parallel nerves of the two preceding species. — Ponds and 
ditches, rare. P. VI. VII. 
15. P. pusillus (L.) ; st. slightly compressed, I. linear 3 — 5- 
nerved, spikes short often interrupted 2 or 3 times shorter than 
their peduncles, nut obliquely elliptical obtusely keeled. — E. B. 
215. — St. slender. L. narrow, rather acute without intermediate 
parallel veins. Spikes compact. — /3. major (Fries) ; 1. broader 
5-nerved, spikes slightly interrupted. P. compressus Sm. E. B. 
418. — P. trichodes (C. and S.) is closely allied to this but has 
setaceous-linear 1., interrupted spikes, and semi-orbicular acutely- 
keeled nuts ; also P. gracilis (Fries) which has subglobose spikes, 
and elliptical-globose nuts without keels. — Ponds and ditches. 
P. VI. 
**** L. all submersed, alternate, linear ; stipules adnate. 
16. P. zosteraceus (Fries) ; I. linear-acuminate obscurely 3- 
nerved with connecting veins, spikes interrupted, nuts (large) 
roundish-obovate rounded on the back with a prominent keel 
when dry. — Fries Nov. ed. 2. p. 51. — This and the two following 
species are very closely allied, but may be easily distinguished by 
attending to the characters derived from the nut. The present 
species approaches the preceding by its leaves. Its nuts are 
2 lines long with a somewhat facial style and a prominent rounded 
keel when dry, but no lateral ridges. — In the Serpentine, Hyde 
Park, London. Dr. J. A. Power. P. VII. E. 
17- P.pectinatus (L.) ; I. linear-setaceous 1 -nerved with trans- 
verse veins, spikes interrupted, nuts (large) roundly obovate 
rounded on the back with two lateral ridges but no keel when dry. 
— L. narrower and more gradually acute than in the preceding. 
Nuts 2 lines long with a somewhat facial style, their back rounded 
and prominent with a ridge on each side but no true keel when 
dry. From the want of authentic specimens I am unable to be 
quite certain of my plant corresponding with that of Fries, Koch, 
&c, for they describe the nut as keeled, which can scarcely be 
correctly said of our plant. — Ponds, scarce. Jersey. Surrey. 
P. VI. ' E. 
18. P.filiformis (Nolte !) ; I. linear-setaceous 1-nerved with 
transverse veins, spikes greatly interrupted, nuts (smaller) obovate 
rugose rounded on the back without keel or ridges when dry. — 
