“ 
84 HYALINIA PURA. 
alert. Moquin-T'andon states that the heart beats with great rapidity in 
this species, but Mr. Watson, who has studied the circulation, has found 
that the pulsations average seventy times per minute when the tempera- 
ture ranges from 60° to 65° Fahr. 
According to Herr Clessin, H. pura is not so predatory and carnivorous 
as the larger species of the Huhyalinia group, but restricts itself more 
particularly, or indeed almost exclusively, to a vegetable diet. 
Geological Distribution.—/Hyalinia pura has not hitherto been 
found beneath the Pleistocene beds, either in this country or abroad. 
Pieistocenr.—<According to Prof. R. Tate, this species has been found 
in the fossil state in the Pleistocene freshwater marls of Copford, Clacton, 
etc., in North Essex. ; 
In Germany, it is recorded by Herr Clessin as very rare in Pleistocene 
alluvium at Piirklgut, and as plentiful in tufa beds near Regensburg, 
Bavaria ; and Prof. E. von Martens notes its occurrence in the diluvial 
beds of ‘Thuringia. 
In France, M. Locard records it from the Mid-Pleistocene deposits at 
Celle, in Seine-et-Marne, and also from those of Upper Pleistocene age in 
the Valley of the Somme. 
Hotocene.—In West Kent, Mr. Kennard reports it from rainwash 
deposits of probably post-Roman age at Halling, Otford, and Greenhithe. 
In East Kent, the Rey. R. Ashington Bullen records it from the deposit 
overlying the Head or Rubble drift at Barton Court estate, on the north 
side of the Dour Valley, Buckland, near Dover. 
In Surrey, the same observer discovered it at a depth of two feet in the 
Neolithic deposit at Colley chalk pit, near Reigate; and Mr. Kennard 
reports it from a rainwash of probably post-Roman age at 'Titsey. 
In North Essex, Mr. Miller Christy records it as rare in the Post- 
Glacial black-earth and peat, but common in the overlying Shell-Marl at 
Chignal-St.-James, and as being also found in the Alluvium at Duke’s 
Farm, Roxwell. Mr. French discovered it in the Alluvial Shell-Marl at 
Felstead, and the Rev. A. J. Shaw in the Alluvium of a drain-section in 
“he Marsh,” near the Vicarage, Shalford. 
In Ireland, Mr. R. Standen has discovered examples in the earthy deposit 
about a foot in depth at Dog’s Bay, Galway West. 
In France, Prof. von Ihering records it from the tufaceous deposits ot 
French Switzerland, and M. Fagot has discovered Zonztes nitidosus in the 
grey clays of Hers, in Haute Garonne. 
Variation.—he known range of variation of this species is not great, 
as in addition to the white and horn-coloured forms which have alternately 
been regarded as the type form, only a more depressed variety has been 
described. 
Although the species may perhaps be Jooked upon as_ essentially 
dimorphic, the horn-coloured and the white or colourless form being almost 
equally distributed and common, yet I have deemed it advisable to adhere 
to Mr. Alder’s conception, and retain the white or colourless form as the 
true type of the species, and to therefore regard the horn-coloured speci- 
mens as a variety, differimg in this from the opinion of the late Dr. Gwyn 
Jeffreys, who desciibed the brownish form as the type and distinguished 
the white form as var. margaritacea. 
