144 MESSRS. W. WEST AND G. S. WEST ON 
After carefully considering Turner’s figures and descriptions of Docidiwm elatum and 
D. robustum, we unhesitatingly come to the conclusion that the two are identical. They 
are of approximately the same size, each possesses a slightly undulate margin, and each 
an apex encircled by a ring of precisely similar tubercles. The only possible distinction 
is in the presence of a slight constriction below the ring of tubercles in D. robustum, and 
we have examined sufficient Pleurotenia of this nature to know that such a slight 
variation is of no use as a specific distinction. Moreover, the nature of the tubercles on 
the two plants is the same, and they are practically equal in number in the two figures 
given by Turner (30 in his figure of D. elatum, 16 being visible; and 32 in his figure of 
D. robustum, l7 being visible) In his text, Turner states that D. elatum possesses 
35—40 tubercles and D. robustum 30-34 tubercles, but these statements are not borne 
out by his figures. 
Turner describes his two plants as having a smooth cell-wall, but we have never yet 
seen a Pleurotenium of this class without a finely scrobiculated cell-wall. 
Var. coNJUNCTUM, nob. Docidium conjunctum, W. B. Turn. in K. Sv. Akad. Handl. 
xxv. 1893, no. 5, p. 32, t. 4. fig. 6. Var. minor, marginibus lateralibus cellularum 
plus undulatis. 
Long. circ. 420 u; lat. bas. et apic. 26 u ( Turner). 
Hab. Bengal. 
-— Forma pUPLO-MAJOR. Long. 682-900 u; lat. bas. semicell. 54-69; lat. apio. 
49—62 u. (Pl. 18. figs. 29-32.) 
Hab. Paddyfield between Kosgoda and Urahaighasmahendai, Ceylon. 
The form seen from Ceylon is about double the size of the plant described as Docidium 
conjunctum, W. B. Turn. It only differs from Pleurotenium elatum, Borge, in its rather 
more undulate lateral margins, and seems to be a form connecting var. conjunctum with 
typical P. elatum. 
It is highly probable that Docidium maculatum, W. B. Turn., and D. cristatum, W. B. 
Turn., are both forms of Pleurotenium elatum, as they seem to us to possess no distinctive 
characters, even the number and nature of the tubercles being the same in each of those 
“ species " as in P. elatum. 
94. PLEUROTJENIUM HYPOCYMATIUM, West & G. S. West, in Trans. Linn. Soc., ser. 2, 
Bot. vol. v. 1896, p. 234, t. 13. fig. 1. 
Var. ANGUSTUM, var. n. (Pl.19. figs. 3, 4.) Var. minor, semicellulis angustioribus, 
inflatione basali prominentiore, lateribus superioribus rectis parallelis, undulis prope 
basin solum. 
Long. 321-334, ; lat. ad bas. semicell. 12-12:5 4; lat. ad apic. 8:5 p. 
Hab. Padddfields, Heneratgodha. 
95. PLEUROTEZNIUM INDICUM, Lund. in Nov. Act. Sci. Upsala, ser. 3, viii. 1871, 
p. 90. Docidium indicum, Grun. ‘Diatom. u. Desmid. Insel Banka,’ in Raben- 
horst's Beiträge zur Kenntniss und Verbreit. Alg. Leipzig, 1865, Heft 2, p. 13, t. 2. 
fig. 18. 
