270 



PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



* Helix lac tea, Miill. 



* ,, nemoralis, L. 



* ,, Plsana, Miill. 



* ,, platy chela, Menke. 



* ,, pomatia, L. 



* ,, punctata, Miill. 

 ,, splendida, Drap. 

 ,, sylvatica, Drap. 



,, vermiculata, Miill. 

 *Placostylus yEsopus, Gass. 



* ,, jihratus, Mart. 

 ,, senilis, Gass 



,, Ouveanus, Mouss. 

 Orthalicus regina, Per. 



,, undatus, Brug. 

 Rumina decollata, L. 

 Ena detrita, Miill. 

 Fupa avenacea, Brug. 



,, Bigorriensis, Charp. 



,, Brauni, Rossm. 



,, muscorum, L. 

 Achatina panthera, Fer. 



,, virginea, Brug. 

 Cochlicopa tridens, Pult. 

 Cionella lubrica, Miill. 

 *lSuccinea elegans, Risso. 



* ,, Pfeifferi, Rossm. 

 Limncea limosa, L. 



,, ovata, Drap. 

 „ paliistris, Drap. 



* ,, pereyra, Miill. 



* ,, stagnalis, L. 



Planorbis complatiatus, L. 



,, spirorbis, L. 

 Campeloma decisa, Say. 

 Valvata piscinalis, MiiU. 

 Vivipara vivipara, L. 



* ,, sp. iudet. [in B.M., juv., from 



China]. 



Neritina flaviatilis, L. 



Ericia elegans, Miill. 



*Pomatias crassilabrnm, Drap. 



,, obscurum, Drap. 



,, patulum, Drap. 



* ,, septemspirale, Raz. 

 Bitropis planorbis, Blanf. 



* Biplommatina catathymia, Sykes. 

 *Acme lineata, Drap. 



* Valuta scapha, Gmel. 

 *Marginella conoidalis, Kien. 



* ,, curt a, Sby. 



* ,, limbata. Lam, 

 ,, miliacea, Val. 



* ,, sp.indet. [group of awM«, Val.]. 

 *Murex secundus. Lam. 



,, trunculus, L. 

 *Bucciniim iindatum, L. 



Purpura lapillus, L. 

 *8ipho antiqims, L. 

 * Tarbinella rapa, Gmel. 

 * Littorina litorea, L. 



* ,, rudis, Maton. 

 *Olivella oryza. Lam. [Brit. Mus.]. 



Dextkal Forms of normally Sinistral Species. 



Clausilia perversa [? L. or Pfr.]. 



,, plica ta, Drap. 

 * ,, plicatula, Drap. 



,, Stentzi, Rossm. 

 Pupa perversa [? author], 

 Physafontinalis, L. 



Ena quadridens, Miill. 

 Clausilia Almissana, Kiister. 



,, bidens, Drap. 



,, bidentata, Strom. 



,, biplicafa, Mont. 



,, Euboisi, Charp, 



„ Macarana, Zgl. 



Amongst the Pelecypocls a similar occuiTence has been observed. 

 Chama is said to be frequently reversed, and a reversed Tellina plicata, 

 with the hinder fold of the shell bent to the left, has been recorded 

 by Fischer.' Jeffreys states that Astarte compressa and A. triangularis 

 sometimes have the hinge reversed, i.e., the right teeth being in the 

 left valve, and vice versa. 



The question naturally arises, what is the cause of this curious 

 inversion ? Dealing only with the Gastropoda two points are clear ; 

 firstly, that it must arise from a cause common to a very large number 

 of species, and, secondly, that the cause takes effect in the early 

 stages of development, ere the protoconch is formed. One explanation 

 suggested has been the effect of the presence of abundant electricity in 

 the air ; another writer, stating that sinistral and dextral forms of 



1 Journ. Conchy!., vol. xxviii, p. 234, 



