1907] Cushman,— New England Species of Pleurotaenium 101 
A SYNOPSIS OF THE NEW ENGLAND SPECIES OF 
PLEUROTAENIUM. 
JOSEPH A. CUSHMAN. 
(Plate 75.) 
Waite the New England desmids have had much less attention 
given to them than has been given to those of the British Isles, there 
are nevertheless ten species of Pleurotaenium known from New Eng- 
land. ‘There are but nine species of Pleurotaenium given in Wests’ 
British Desmids. Four of our species have not been reported from 
the British Isles. The species are all comparatively large and con- 
spicuous and are easily distinguished from one another. ‘They fall 
naturally into three groups. The majority of the species of the genus 
have straight sides or in certain cases slightly undulate. ‘The species 
of the second group including P. nodosum and P. constrictum have 
definite enlarged portions or annulations. The third group is repre- 
sented by the single species P. verrucosum, which has the surface 
divided into rectangular areas in more or less distinct rings. Our 
species with their several varieties are given below and their distri- 
bution in New England as far as known. The records followed by an 
exclamation point are those from which specimens have been seen 
by the writer. In most points the recent monograph of the Wests 
has been followed. A key to the New England species is given here, 
based in part upon that of the Wests. 
PLEUROTAENIUM Nägeli, 1849. 
Cells cylindrical, circular in end view, sides straight or somewhat 
sinuate; semicells with a basal inflation and often with secondary 
ones distally, apex truncate, usually with a ring of tubercles; chloro- 
plasts several, in irregular longitudinal bands parietally arranged. 
KEY To THE New ENGLAND SPECIES OF PLEUROTAENIUM. 
I. Cells cylindrical or slightly attenuated, end view circular, sides nearly 
straight or very slightly sinuate toward the base of the semicell, or evenly 
curved from base to apex, not prominently sinuate and without a thickened 
surface pattern. 
