THE FRESHWATER PLANKTON OF THE SCOTTISH LOCHS. 495 
forms of this species from the plankton of Sweden (wde Lemm. in Archiv f. Bot., 
Bd. ii., No. 2, t. 2, f 1-49). We have found all these forms in the Scottish plankton, 
and cysts occur plentifully. Figs. xylogr. 1, B and D, are from specimens observed in 
plankton from the Shetland Islands. Fig. 1, B, shows the first appearance of the third 
antapical horn (at,), and fig. 1, D, shows the maximum development and divergence of 
the three antapical horns. 
Peridinum Westw, Lemm., sp. n. 
Body nearly globular, at sie posterior margin slightly sinuate, 44-45 long and 
42°5-59u broad, in the girdle-view (fig. xylogr., 2, C and D) nearly reniform, divided by 
the transverse furrow into two nearly equal halves. Transverse furrow disposed in a 
conspicuously spiral manner (vide fig. 2, A). Longitudinal furrow reaching a short 
distance into the apical half and downwards as far as the posterior margin of the body, 
in the posterior part much dilated, and in the middle of the left margin with a blunt 
papilla. Membrane ornamented with irregular, undulating, and sometimes ramified 
ridges. 
Plates BE Aianly developed, in the lower part of the body much larger than in 
the upper part. Hpivalve (fig. 2, C) with a transversely elongated rhomboidal plate ; 
equatorial plates seven, the dorsal one much larger than the others; first apical plate 
quadrangular, dilated outwards ; second apical plate pentagonal, nearly as long as broad ; 
third apical plate on the dorsal side of the first dorsal plate, forming part of an apical 
eirele of plates; fourth apical plate irregularly quadrangular ; first dorsal plate nearly 
triangular, situated at the apex of the upper part of the body; second dorsal plate 
trapezoid ; apex wanting. Hypovalve (fig. 2, D) with two antapical plates, of which the 
right one is the larger; suture between these plates running from the middle of the 
ventral margin obliquely towards the left dorsal side. 
Intercalary strips of the carapace very variable, in old cells sometimes very broad. 
Hab.—Lochs Bairness and Shiel, Inverness ; Loch Rosque, Ross; Loch Shubhaill, 
Lewis, Outer Hebrides. 
1350 
ue et 
% Saha <p 
Fic. 2 
Peridinium Westii, Lemm. x 610. A, ventral view; B, dorsal view; C, Epivalve ; D, Hypovalve. 
(After drawings by LEMMERMANN.) 
P. Westi is distinguished from any other species of Peridiniwm by the disposition 
of the plates and the curious ridges of the membrane. 
