296 THE FRESH-WATEK LOCHS OF SCOTLAND 
together when made for such Hght as they can yield us, and for 
suggestions as to future work. 
As to the distribution of the great majority of the 724 species 
recorded in the hsts, it must be said that very little is known. The 
littoral region, where life is most abundant, has only been occasionally 
studied. Many of the species are only once recorded, yet there is no 
reason to believe them rare. The species which are cosmopolitan or 
generally distributed are indicated by the word " general" in the lists. 
The distribution of the majority of the species will not be dealt 
with at all. In this place there will be studied in detail the distribu- 
tion of a few species which are fairly well known, and are not of 
general occurrence, and some which are very local or rare. In dealing 
with some little-known species, such indication as is possible will be 
given of their world-distribution. 
ZOOPLANKTON 
Mollusca. — Of the two large bivalves in the lochs, U7iio Marga- 
ritifer (L.) is the general species in the Highland lochs, and Anodonta 
cygnea (L.) is the Lowland species. 
Hydrachnida. — Lehert'm tau-insignita (Lebert). This species, 
discovered in the Lake of Geneva, in the abyssal region, is common in 
Scotland, and is not solely abyssal in this country. It was supposed 
to be one of those forms which found analogous conditions in the 
littoral region of northern lakes, and in the abyssal region of more 
southern lakes. Several other animals are in the same category. 
The recent discovery that the British species, recorded under the 
name of L. tau-insignita^ is really some other species, modifies this 
view. All the records, therefore, require revision. 
Hidtfeldtia ?^ectipes, Thor. — A northern species, inhabiting (so 
far as previously known) only Scandinavia. In Scotland it has only 
as yet been recorded for Orkney, where it was discovered in 1906. It 
is there the commonest species. 
Tardigrada. — Echiniscus gladiator, Murray. — Pretty widely 
spread in Scotland, and not peculiarly lacustrine ; it is now known 
from the Faroes (Sellnick), somewhere in the Pacific region (Richters), 
and British Columbia. 
E. ivendti^ Richters. — Scottish and Arctic. Richters doubts if 
the animals in these two regions are the same. 
E. spHshergensis^ Scourfield. — Scottish and Arctic. Pretty widely 
spread in Scotland. 
Macrohiotus ambiguus, Murray. — Scottish, Swiss, and Arctic. On 
ground-moss and lake margins in Scotland ; on a deeply submerged 
moss (abyssal) in the Lake of Geneva. 
