23 
Upper leaves 3-4 inches long, alternate (or occasionally opposite), 
elliptical, coriaceous, with 14-16 principal ribs, and occasionally 
secondary ones which fall short of the apex and anastomose with 
the cross-veins; areolation distinct over the whole leaf; petioles 
` 2-6 inches long. Peduncles 2 inches long, slightly thickening up- 
wards. Fruiting spikes 1-1 % inches long, rather few flowered.” 
The fruit of this species is very distinct. Drupe 2 lines long, 
1% lines wide, strongly tricarinate, the middle keel prominent, 
sharp and denticulate, while the lateral keels are strikingly em- 
bossed with protuberances; face slightly curved; style stout, short, 
facial. 
Named and described from specimens in the Herbarium of the 
British Museum collected by Schmitz in the valley of Myrica, 
Mexico, and at Berlin collected by Schaffner, Aug., 1854, in a 
river near Chasseltepec, Mexico. (Plate XXXIII. The figure of 
the plant is from a drawing of Mr. Bennett.) 
` IO. POTAMOGETON HETEROPHYLLUS, Schreb. Spicileg. Fl. Lips. 21 
(1771). : 
P. gramineus, Vries, Nov. Ed. 2, p. 36 (1828), not L. 
P. gramineus, var. heterophyllus, Fries, Nov. Ed. 2, p. 35 (1828). 
A very variable species. Stems slender, compressed, much- 
branched, from 1 to 2 feet high, usually growing in quiet water. 
Floating leaves coriaceous, oval or elliptical, short-pointed at the 
apex and rounded or sloping at the base, occasionally sub-cordate, 
8 lines to 1% inches long and 4-6 lines wide, with 10-18 nerves; 
petioles 1-4 inches in length. Submerged leaves pellucid, sessile, 
lanceolate or linear-lanceolate, acuminate or cuspidate, those of 
the type rather stiff, 1-3 inches long and 1-6 lines wide, with 3-7 
nerves, the uppermost often petiolate. Peduncles often thickened 
upwards, 1—4, rarely 7, inches in length, often clustered at the top 
of the stem. Stipules loose, spreading, obtuse, 2-keeled, 8-12 
lines long. Spike 34-114 inches long, usually fruiting freely. 
Fruit roundish or obliquely obovate, 34-177 lines long by 34-1 
line broad, slightly curved or angled on the ventral side, rounded: 
and indistinctly 3-keeled on the back, the obovate forms with an 
inward basal curve on the face and an indentation running into it 
. from the centre of the sides; style short, obtuse, apical, rarely 
