—— 
THE DIATOMACE-E OF THE HULL DISTRICT. 159 
F.L.S. and G. S. West, A.R.C.S., which has just appeared. 
We have, however, rejected a few included by them on the 
authority of Norman, on one of two grounds; either that 
having examined Norman’s gatherings, we find that he had 
mis-named the species recorded, or that we do not admit the 
forms recorded as worthy of specific identification. 
In the identification of Norman’s records we have been 
greatly assisted by the kind permission of the authorities of 
the Hull Municipal Museum to inspect the slides formerly 
forming his collection and now in their possession. 
The comparison of these slides with present day gatherings 
leads to some noteworthy considerations. The firstis perhaps 
the great industry and patience of Norman and his contem- 
porary microscopists, as evidenced by the number of localities 
they have examined and the exhaustive lists from each place. 
The next most striking fact is the remarkable fixity of certain 
species in certain localities. Half a century has rolled away 
since Norman and Harrison made their records, but still the 
springs of Newbald yield Melosiva arenaria, and those of 
Haltemprice, /ragillaria Harrisoniz,—in each case the only 
localities in this district where these forms are found in quantity. 
And now, as in those days, all Humber gatherings still contain 
Pleurosigma angulatum, Amphiprora alata and Nitsschia sigma 
with its varieties. Side by side with these we find other cases, 
illustrative of the apparently capricious appearance and dis- 
appearance of certain species which every diatomist must 
have experienced. For instance, in the Wold springs of 
Newbald and Weedley, Dzatoma hyemale is now a fairly 
common form, but it is not recorded by Norman and we fail 
to find it in any of his slides, though he has made many pre- 
parations from localities where it may be found to-day. A 
converse case of disappearance is shown in Norman’s 
“« Amphiprora constricta,”’ which, after considerable hesitation 
and research of authorities we make out to be S¢auronezs 
amphoroitdes Grun, though it is not exactly typical. This 
seems to have been not uncommon in Norman’s time in the 
docks of Hull and Grimsby, but we have failed to find it now 
in those localities. Mavicula peregrina and N. digito-radiata 
var Cyprinus, common in most of Norman’s slides of brackish 
water forms, are much scarcernow. Many of our new records 
are from the brackish waters from the Hull and Humber, such 
as Aulacodiscus Sollittianus and Campylodicus clypeus, but 
these are not at all plentiful, so it is not necessary to suppose 
that they are fresh arrivals, but merely that Norman did not 
happen to light on them. 
