494 
MR W. WEST AND MR G. 8S. WEST ON 
Ceratium hirundinella, O. F. Miiller. 
The abundance of this organism is one of the most conspicuous features of the Scot- 
tish plankton, but suttcient observations have not been made to decide definitely the 
time of its maximum period. 
The length and divergence of the antapical horns are exceedingly variable. 
LEMMERMANN gives the following measurements :— 
Tenecice Length of | Length of | Length of Total | — 
Locality. a ae |Ist Antapical] 2nd Antapi-| 3rd Ant- Length of | — 
pical Horn. : 
Horn. cal Horn. | apical Horn. Body. | 
Loch Cuthaig, i 103u 68-5 44. 15p 2345p 
Loch Roinebhall, Lewis, 96-1096 | 72-85p 33-42 Tp 212-245°6y | 
Loch Shubhaill, f : 105-124 60-93 37-545 py 4-15 py 2105-281! 
Loch Diracleet, : 103-lllp 82-104u 34-49 15-234 238-291u | 
Loch a Mhorghain, Harris, 101-153p 86-1204 45-60 15-30 251-357 
Loch Laxadale, : 105-120°54 | 73-103u 40-45 15-31°54 | 237-304p |] 
To these we add two others— 
Loch Ruar, Sutherland, 86 46u Qhp 0 1984 | 
Loch Fadaghoda, Lewis, 118-129 67-82 60-67 31-38 235-260u | 
In the specimens from Loch Ruar there was a complete absence of the third (short) 
antapical process, and in those from Loch Fadaghoda the three antapical processes were 
nearer a uniform development than in any other specimens examined. 
Fig. 1. 
A, from Loch Ruar, Sutherland ; B, from Loch Asta, Shetlands; C, 
Ceratium hirundinella, O. F. Miiller. 
from Loch Fadaghoda, Lewis; D, from Loch Beosetter, Bressay, Shetlands. 
horn ; at,, at,, ats, the three antapical horns. 
(All x 200.) ap, apical 
In fig. xylogr. 1, A, the third antapical horn is absent, but in fig. 1, D, it has reached 
its maximum development (at,). _LEMMERMANN has figured a large number of different 
