The representative form of A. clausi, which we have here, is a dominant 
index type in Hudson Bay and on the North Atlantic and North Pacific coasts, 
and for this form the varietal name of hudsonica is proposed. This discrimina- 
tion is of interest, not because of the trivial characters involved, but in con- 
nection with the correlation of ecological conditions on both sides of the North 
Atlantic Ocean, as well as upon the opposite eoasts of the North American 
Continent. 
26. Miss K. E. Carpenter.—On the Biological Factors involved in 
the destruction of River-Fisheries by Pollution consequent on 
Lead-mining. 
An account of a preliminary investigation of this subject in the Aberystwyth 
District of Cardiganshire was submitted to Section D at the Hull meeting of 
1922, when attention was drawn to the fact that circumstantial evidence, collected 
in the course of a field-survey, seemed to tell against the popular theory of direct 
extermination of fishes by the clogging of their gills by adherent galena-particles, 
in favour of an alternative hypothesis, newly suggested by the author—that of 
the efficacy of extremely dilute solutions of lead-salts, such as occur in the 
polluted waters of the local rivers Rheidol and Ystwyth. 
Since that date full-time investigations have been carried on with the aid of a 
grant from the Department of Scientific and Industrial Research ; experiments 
in field and laboratory have established the following facts :— 
_ (a) Fishes can live, and apparently suffer no injury, in direct contact with 
lead-containing river-grit and lead-containing sediment taken directly from a 
mine dump. 
(b) Fishes can live in the polluted River Rheidol itself for long periods 
during calm weather. 
(c) They die soon after the onset of a flood-period, without symptoms of 
inflammation or bruising of the gills or other external parts. 
(d) The Rheidol water at such a season contains measurable quantities of 
lead in solution—no such substances can be detected in it during the calms. 
(e) The ‘ flood-water,’ when filtered and used in the laboratory, is fatal to 
fishes and to invertebrate species selected as typical of the local freshwater 
fauna. This quality is not due to the degree of hydrogen ion concentration, but 
to its dissolved content. 
(f) The neighbouring rivers, Teifi and Meurig, though affected until recently 
with lead-mining near their banks, are rich in fish-life—trout, minnows, stickle- 
backs, and salmon occur in these waters. 
(g) The sediments from these two rivers contain lead-grit, but their waters, 
even in flood-time, contain no appreciable amount of lead in solution. 
The effective agent in the destruction of local river fisheries is clearly indi- 
cated, and the old precaution of ‘ sedimentation,’ which aimed at keeping lead- 
grit out of the rivers, is seen to be futile; a new method of treatment may be 
suggested in outline, for elaboration by the technical expert. 
SECTIONAL TRANSACTIONS.—D. 403 
; 
27. Mr. BE. Meuvitte Du Porte.—Some Endophytic Protozoa. A 
; contribution to our knowledge of the Protozoa living in the latex 
of plants. 
A survey made in 1923 revealed the presence of amcebz and flagellates in the 
latex of ten species of common plants and several exotic plants. The organisms 
have been shown to hibernate as minute resting cells in the overwintering stems 
and roots of their hosts. They have been shown to pass into the seeds of 
_ Asclepias syriaca and infect the seedlings. Results of morphological, cultural, 
and transmission studies will be given. 
28. Prof. E. M. Waker and Miss Norma Forp.—Some Features in 
the Anatomy of Grylloblatta, a primitive Orthopteroid Insect. 
Grylloblatta, a remarkably synthetic genus of Orthopteroid insects discovered 
by the senior author in 1913, combines characters of most of the lower pterygote 
DD2 
