542 MR. W. WEST AND PROF. G. 8S. WEST ON 
In its general form A. crassus might be compared with A. con- 
‘roversus, West, but the exceedingly small size and delicacy of 
the latter is sufficient to distinguish it. The vertical view is also 
broadly elliptical, whereas that of A. crassus is fusiform-elliptic. 
13. ARTHRODESMUS QUIRIFERUS, sp. n. (P!. 17. figs. 9, 10.) 
A. submagnus, paullo longior quam latus (sine spinis), modice 
constrictus, sinu latissime aperto et rotundato vel interdum 
extremum versus angustiore ; semicellule subtriangulares, mar- 
ginibus lateralibus convexis, apice late concavo, angulis spina 
valida longissima recta divergente instructis; a vertice vise 
elliptic, polis cum spina valida longissima ; cellulis fere tortis. 
Long. sine spin. 28-31 p; lat. sine spin. 25-26 »; long. spin 
31-44 p; lat. isthm. 6-9°5 yw; crass. 10-11 p. 
Hab. Loch Shin, Sutherland ; Loch Laxadale, Harris, Outer 
Hebrides. 
This species occurred in prodigious quantity in the plankton 
of Loch Shin. It is distinguished from the biradiate form of 
Staurastrum jaculiferum by the outward form of the cells, with 
retuse apices, and by the longer spines. One of its most con- 
spicuous features is the torsion of its cells, which appear to be 
twisted at the isthmus. The specimens showed a certain amount 
of variability. 
14. A. rRIANGULARIS, Lagerh. in Ofvers. af K. Vet.-Akad. 
Forh. (1885) no. 7, p. 244, t. 27. f. 22.—A. Incus, Hass., var. 
triangularis, Lagerh. in Nuova Notarisia, iv. (1893) p. 182. 
Var. HEBRIDARUM, var. n. 
Var. corpore semicellularum robustiore, apicibus convexis, sinu 
minus aperto, spinis validioribus et paullo longioribus: membrana 
cum scrobiculis parvis et sparsis. 
Long. 32°51; lat. sine spin. 25, cum spin. 845; lat. 
isthm. 85 »; long. spin. 27-81 p. 
Hab. Loch Nan Eun, N. Uist, Outer Hebrides. 
This variety resembles A. triangularis, var. americanus, West 
& G. S. West, more than the typical form, but the spines are 
much stouter and longer. It should also be compared with 
A. Incus, var. subtriangularis, Borge (in Botan. Notiser, 1897, 
p- 212, t. 3. f. 4). 
-. « 
a. 
