i. 
>, 
SCOTTISH FRESHWATER PLANKTON. 541 
Var. zruiopicum, West & G. S. West, in Journ. Bot. xxxv. 
(April 1897) p. 114. 
Long. 69 »; lat. 61; lat. isthm. 28; crass. 40. (PI. 15. 
fig. 7.) 
Hab. Loch Shin, Sutherland. 
10. C. Caprrutum, Roy § Biss. in Journ. Bot. xxiv. (1886) 
p- 195, t. 268. f. 9. 
Var. @R@NLANDICUM, Borgesen, Ferskv. alg. Ostgrénl., Med- 
delelsen om Gronl. 18, Kjébenhavn, 1894, p- 16, t. 1. f. 5. 
Long. 28-31 p; lat. 25 pw; lat. isthm. 9-115; crass. 16 pz. 
(Pl. 15. fig. 5.) 
Hab. Loch Doon, Ayrshire. 
11. C. apBreviatum, Racib. in Pamietnik. Wydz. matem- 
przy. dkad, Umiej. Krakow. x. (1885) p. 83, t. 10. f. 13. 
Var. major, angulis superioribus rotundatioribus. 
Long. 20-28 p ; lat. 22-29 »; lat. isthm. 5°5-8 w; crass. 10°5- 
3p. (Pl. 15. fig. 6.) 
Hab. Loch Shin, Sutherland. Ioch Mor Bharabhais, Lewis 
Outer Hebrides. 
Genus ArrHropesmus, Ehrenb. 
12. A. crassus, sp.n. (PI. 14. figs. 8, 9.) 
A. parvus, circiter tam longus quam latus (sine spinis), modice 
constrictus, sinu latissime aperto leviter acuminato; semicellule 
obverse subtriangulares, marginibus lateralibus levissime con- 
vexis, apice late convexo, angulis acutis spina brevissima instructis ; 
a vertice vise late elliptico-fusiformes, polis acutis cum spina 
brevissima. 
Long. 21-24; lat. (sine spin.) 19-23; long. spin. 15, ; 
lat. isthm. 9-5-12°5 pw; crass. 13 p. 
Hab. Loch Mor Bharabhais, Lewis, Outer Hebrides. 
This plant is of the same size as A. psilosporus, Nordst. et 
Lofgr. (in Wittr. & Nordst. Alg. Exsic. 1883, no. 558), but is 
relatively shorter, and the semicells are never retuse either at 
the sides or the apex; the vertical view has also more acute 
poles. 
It is distinguished from A. Phimus, W. B. Turn., by its more 
robust aspect, its convex apices, much shorter spines, and its 
greater thickness in the vertical view. 
2s2 
