28 THE SCOTTISH NATURALIST 
FEEDING OF THE PEA CRAB.—Though the Pea Crab (Pinnotheres 
pisum) is a common inhabitant of mussels and cockles—it is often to be 
seen within Horse Mussels on the shore of the Firth of Forth—its mode 
of feeding has never been scrutinised, and its relationship with its host 
has been attributed to the series of beneficent partnerships which help, 
without hindering, each of the parties to the compact. Now Dr J. H. 
Orton (Mature, 23rd December 1920) has solved the question by making 
a window in the shell of a mussel, and through this keeping a close 
watch on the actions of the crab within.- It was found to lay hold on 
and devour the strands of minute organisms collected for food from the 
sea water by the mussel, while these were passing along the gills towards 
the mussel’s mouth. No benefit done by the crab to the mussel in 
return for this free shelter and food could be discovered, so that the 
relationship of the creatures appears to be that rather of host and 
parasite than of helpful co-operators. Dr Orton also discovered that in 
their earlier stages the female Pea Crabs resemble the smaller male 
forms. 
DIPTERA STUDIES.—After comparative neglect for a long term of 
years, British Diptera, or Two-winged Flies, appear to be receiving 
more of the attention their diversity of organisation and habits deserve. 
We notice not only an increasing number of local lists, but also of 
articles on special groups, which will undoubtedly inspire and encourage 
beginners in an interesting study. In the two last published numbers 
of the Extomologists’ Monthly Magazine we note an excellent list of the 
Diptera of South Shropshire by Herbert Bury (pp. 249-256), comprising 
240 species, collected in three localities only, and including some note- 
worthy rarities. On pp. 264-270 F, W. Edwards, of the British Museum, 
an acknowledged authority on the Nematocera, publishes a valuable 
account of the British Chaoborine and Dixinz, which may be regarded 
as supplementing Lang’s Handbook of British Mosguttoes, recently 
published by the British Museum. And in the December number 
(pp. 270-276) J. E. Collin presents an admirable account of the 
Sylvaticus-group of the genus Pzpunculus, with an up-to-date key for 
determining males and females of the group known to occur in Britain. 
IMMIGRATION OF RED ADMIRAL BUTTERFLY IN 1920.—Several 
notes have lately been published which point to an unusual immigration 
of the Red Admiral Butterfly (Pyramezs atalanta) to this country. In 
this connection two notes appearing in the November number of the 
Entomologist (p. 261) record the occurrence of the species in Scotland. 
Mr A. E. J. Carter reports a specimen seen about the middle of 
September, two on the 26th of the same month, and a very fine large 
one on 3rd October—all in bis garden at Monifieth. In his experience 
these constitute the third occasion only on which he has seen it during 
the last thirty years. In the west coast Mr A. Steven Corbet saw an 
example at Tarbet, Loch Fyne, on 22nd September, but this was the 
only specimen noted during a stay of two months in the Clyde 
district. 
