32 THE ZOOLOGIST. 
It would greatly facilitate study if leading conchologists would discuss the 
matter with the view of coming to some determination as to what should 
be considered a species, a subspecies, or a variety, and then to formulate 
standard rules for the guidance of collectors. If we could discover the 
causes of variation, we should be able to judge whether any particular form 
was likely to gain ascendancy in the struggle for existence, remain at 
a standstill, or drop out of the race. As to colour-variatious, these may be 
much more important than they are assumed to be. The existence of 
many species may depend upon colour. There is a strong tendency 
amongst Mollusca, as well as amongst other creatures, to exhibit the colour 
of the soil or other surroundings in or on which they live. In Craven, 
where there are few hedges, I have noticed that very many individuals of 
Helia rufescens are of a greyish colour, assimilating to that of the walls on 
which they are found ; whilst in the flatter and more wooded parts eastward 
they are dark brown or rufous, corresponding with the colour of rotten bark 
or decayed leaves. On the red clay or sand the red or reddish-brown shells 
of Helia nemoralis predominate over other colours. ‘The similarity in form 
of the shell of Claustlia laminata to the elongated bud of the beech has 
been often noted. In my opinion our brightest coloured shells are 
becoming obliterated, or are gradually assuming the colours of the soil 
or rocks on which they are found. Mr. Woodward states (p. 412) that 
thin shells are the result of a deficiency of lime. I should rather think 
that thin shells are those which have only just arrived at maturity, and that 
they will thicken with age. I have found some very thin adult shells of 
both Helia nemoralis and aspersa on soil that was all lime, and very thick 
ones where there was next to none.—G. Roserts (Lofthouse, Wakefield). 
PS. At p. 475, in the last number, the words “ to be continued” have 
inadvertently appeared, the article being concluded. 
SCIENTIFIC. SOCIETIES. 
Linnean Soctety or Lonpon. 
November 19, 1885.—Prof. Mosrney, F.R.S., in the chair. 
Mr. A. D. Michael exhibited and described the remarkable nymphal 
s tage of Teyeocranus cepheifornis, a species of the group Oribatide, which 
he lately discovered for the first time in England. He has furthermore 
succeeded in tracing the whole life-history of this animal. The creature in 
its nymphal stage is exceedingly strange and beautiful. It carries on its 
back as concentric shields the dorsal portion of all its cast-skins, and these 
are bordered by projections each bearing a rose-leaf-like cuticular process of 
transparent membrane with chitinous nervures. ‘The drawing of the nymph 
was first sent to Mr. Michael, two years ago, by Herr Pappe, of Bremen. 
