Liver Rot of Sheep 
236 
Several streams following a similar course to the above unite and 
empty into the sea at Clarach Bay 1|- miles N. of Aberystwyth. The 
two chief rivers of the Area however, are the Rheidol and Ystwyth. 
The first mentioned is formed from the streams Carndwr, Llechwedd- 
mawr, Hyddgen, Hengwm, etc., upon the slopes of Plynlymon and the 
adjacent mountains, and after taking a southern course for some eight 
miles turns westward at the Devils Bridge. The Ystwyth rises among 
the mountains south of Plynlymon, and, like the Rheidol, reaches the sea 
at Aberystwyth harbour after a course somewhat similar and parallel 
to that river. In the extreme s.e. of the area the watershed of the 
Teify is reached and, southward the gorge of the Wyre Stream, prac¬ 
tically forms its boundary. 
The rainfall of the Area is considerable and varies greatly in the 
different districts. It will be considered in connection with the bionomics 
of L. truncatula. From the point of view of the Agricultural Zoologist 
the Area surveyed is divisible into six chief divisions each with its own 
typical pests and diseases. 
Natural Divisions of the Area. 
These are approximately outlined in Map I, and are as follows: 
( a) The great central mountain mass of the High Plateau, chiefly 
natural sheep pasture; very lightly populated and with a heavy rainfall. 
The typical troubles of this region are Gid in sheep and cattle and 
Fox damage to lambs. 
( b ) The Fall Line or Fridd, typified by rough hillsides and ravines, 
often wooded, the chief diseases are Bovine Piroplasmosis; Sheep 
Maggot; Liver Rot; Pigeon damage, Warbles, etc. (This passes in 
turn from n. to s. into the following.) 
(c) The Dyfi Flats, also known as Y Gors Fochno, or Borth Bog; 
a flat largely undrained area of peat, salt marsh and alluvial pasture 
with here and there rocky eminences or “ Islands ” (Ynys). The 
region is bordered on the n.w. by the river Dyfi, on the w. by sand 
dune and storm beach, and on the e. by the last mentioned Fridd 
(here heavily wooded) and to the s. by the next type. The chief com¬ 
plaints are Bovine Piroplasmosis, Liver Rot, Sheep Maggot and Fox 
damage. 
(d) Coastal Lowlands : a comparatively highly cultivated farming 
area, lying chiefly around Aberystwyth, and bounded on the N. by the 
Dyfi Flats, on the E. by the Fridd, Westward by the sea and to the s. 
passing into the next type (e). The bulk of the dairy farming of the 
