316 MR. G. 8. WEST ON SOME BRITISH 
without the spines. It was observed in many varied localities 
up to 3000 ft. on Snowdon, N. Wales, and 3000 ft. in Scotland. 
Although this animal was first described by Ehrenberg as a 
species of Arcella, and is yet regarded as such by some authors, I 
think there can be no doubt that it bears a closer resemblance to 
Diffiugia constricta than to any other testaceous Rhizopod. 
Leidy poiuts this out most clearly, and gives illustrations of 
numerous intermediate forms, and Blochmann also comments 
upon it. 
From near Knaresborough and from near Giggleswick, W. 
Yorkshire, a large number of small examples were seen with the 
shells composed of sand-grains. The shells were very much 
oblique, and possessed three smooth, chitinous spines at the 
fundus, each spine being sharply apiculate. Diameter of shell 
63 «3 length of spines 25 p. 
A peculiar form was met with from Widdale Beck, N. York- 
shire, with fourteen spines arranged in an arc, those at the 
fundus being very short, and those towards the mouth very long. 
Diameter of shell without spines 190 p. 
Some striking forms were observed from Terrington, N. York- 
shire. The shells were thin, chitinous, and almost transparent. 
Diameter of shell 120 ». Three short, thick spines were present, 
each spine being perforated at the apex. Thus, in addition to 
the mouth of the shell, there were three open, tubular passages 
placing the interior of the shell in communication with external 
surroundings. Owing tothe thinness and transparency of the 
shells, I was enabled to carefully examine the structure of 
the chitinous membrane of which they were composed. Leidy 
remarks (loc. cit. p. 188) that “while spineless specimens of 
Centropyxis, composed of chitinoid membrane, approximate to 
Arcella in character, I never could satisfy myself that the shell 
of the former exhibited the cancellated structure of the latter. 
In some chitinous shells of Centropyxis I have observed a 
punctated appearance of some uniformity, but it did not display 
the clear cancellated arrangement so characteristic of the shell 
of Arcella.” 
The chitinous membrane composing the shells of the Terring- 
ton forms was of a pale yellow colour and minutely scrobiculate, 
The scrobiculations were irregularly disposed, being scattered 
more or less in groups, and between them were numerous much 
