SYKES : VAKIATION IN RECENT JIOLLUSCA. 



269 



recorded the occurrence of four young sinistral shells from a normal 

 dextral female of Campeloma decisa, Say ; whilst Miss Hele noted the 

 occurrence of dextral young from a sinistral Helix aspersa. On the 

 other hand, sinistral Limncea stagnalis have been bred from a sinistral 

 parent, and in a pond in Belgium adult sinistral specimens of this 

 species were found in one year, whilst in the following year similar 

 young shells were taken, this leading to the suggestion that these 

 latter were descendants of the former. I think the evidence amounts 

 to this, that a sinistral parent shell is not unlikely to have sinistral 

 young, but this result may not follow. It may be remarked, in 

 passing, that in Melantlio 15-25 per 1000 of the embryos are sinistral, 

 but only 1 per 1000 survives. In slugs ^ Limax schwahii, Frauenfeld, 

 has been recorded with the respiratoiy opening on the left side, and 

 Arion rufus, L., with a similar character. 



It may perhaps be of interest to give a list of the shells which 

 I know of recorded as reversed. It is not proposed to deal with the 

 vexed question of ultra-sinistral and ultra-dextral shells, and for the 

 purpose of the moment Plauorbis has been left as dextral. Owing to 

 the scattered nature of the literature this list must be very incomplete, 

 but may form a basis for other workers : no attempt has been made to 

 verify the specific names. 



Sinistral Forms of normally Dextral Species. 

 * All so marked have been seen by the writer. 



*Gihbus Lyonetianus, Pallas. 

 Vitrina pellucida, Miiller. 

 Hyalinia nitida, Miiller. 

 ,, nitidula, Drap. 

 Zonites Alyirus, L. 

 Xesta duplocincta, Bttg. 



* ,, Javatiica, Fer. 

 Laoma Moellendorffi, Suter. 



* Pyramidula alUrnata, Say. 



,, Cooperi, Binn. 



,, humilis, Hutton. 



,, rotundata, Miill. 



,, solitaria, Say. 



,, striyosa, var. 

 Polyyyra elevata, Say. 



,, exoleta, Binn. 



,, fallax, Say. 



,, hirsuta,' Say. 



,, injlecia, Say. 



,, Mitchelliana, Lea. 



,, profunda, Say. 



,, thyroides, Say. 

 Pleurodonte lychnuchus, Miill. 

 Stylodonta unidentata, Chemn. 

 *Acavus hamastoma, L. 



* ,, phoenix, Pt'r. 

 *Dorcasia ylobulus, Miill. 



,, lucana, Miill. 



*Leucochroa candidissima, Drap. 

 Helicella acuta, Miill. 

 ,, apieina, Lam. 



* ,, Cantiana, Mont. 



,, Garthusiana, Miill. 

 ,, cespitum, Drap. 

 ,, conspurcata, Drap, 



* ,, ericetorum, Miill. 

 ,, explanata, Miill. 

 ,, fasciolata, Moq. 

 ,, neylecta, Drap. 



,, oreta, Brgt. 

 ,, trepidula, Serv. 

 ,, trochoides, Poiret. 

 ,, unifasciata, Poiret. 

 ,, variabilis, Drap. 



* ,, viryata, Da Costa. 

 Hyyromia hiapida, L. 



,, limbata, Drap. 

 Vallonia pulchella , Miill. 

 *Seliciyona arbuslorum, L. 



,, cornea, Drap. 



,, lapicida, L. 



,, Qnimperinna, Fer. 

 *Relix apalolena, Brgt. 



,, aperta, Born. 



* ,, aspersa, L. 



* ,, hortensis, Miill. 



1 Cf. Baudon: Journ. Conchyl., vol. xxxii, p. 320. Seibert : Mai. Blatt., vol. xxi, 

 p. 1U8. 



