STANDEN : REVERSED SHELLS I\ THE MANCHESTER MUSEUM. 



visceral organs. Depress the remainder of the spire still more, and 

 now the apex is flush with the rest of the whorls, and lies flat like the 

 spring of a watch. The PAysa-like shell has become a Planorbis- 

 shaped shell ! But now continue the depression of the apex, push 

 it right through to the other side, and the discoid or planorboid shape 

 gives place to an intermediate sub-discoidal form. Continue the 

 process still further, .and you have your Physa-\\V.Q. shell back again, 

 but now with the whorls completely reversed ! The sinistral shell, 

 with its sinistrally placed viscera, first of all passed into what might 

 be called a neutral stage, wherein it was hard to say whether its 

 planorboid shape meant that it was sinistral or that it was dextral ; 

 and from that it emerged into a pseudo-dextral, but really ultra- 

 sinistral shell, but with its viscera still sinistral ! Thus it would 

 appear that the planorboid shape is really a kind of intermediate, 

 half-way house between, on the one hand, sinistrorsity of both shell 

 and animal, and, on the other hand, sinistrorsity of animal, but 

 pseudo-dextrality of shell. Naturalists of an earlier day, such as 

 Lamarck and Deshayes, puzzled with the apparent anomalousness 

 of these phenomena, named the genus Planorbis ' amphidromic,' 

 or 'turning in both directions,' as certain species seemed to choose 

 one course and certain others a reverse direction. But this ingenious 

 theory of 'hyperstrophy,' or the turning of a mollusc inside out like 

 the finger of a glove, entirely explains what before was so obscure.^ 



"This process of turning inside out may take place in either 

 direction ; in other words, there may be ultra-sinistrorsity or ultra- 

 dextrality. The former may be illustrated in the case of two fresh- 

 water genera, Poinpholyx from North America, and Choanomphalus 

 from Lake Baikal ; and the latter by the genera already cited — 

 Li/nadna, Meladoiniis, and Lanistes." 



It may perhaps be added that the subjoined catalogue is a list, not 

 of published records, but of actual specimens. 



NORMALLY SINISTRAL SPECIES. 



Plectopylis plectostoma Be?!s. 



Kha.si Hills, India. 

 Ariophanta cambogiensis Rvc. 



Cambodia. 

 A. brookei Reus. Borneo. 



A. foveata Pf>'. India. 



A. rumphii Gr. Java. 



A. janus Bk. Malacca. 



A. Itevipes Miill. Bombay. 



A. thyreus Bens. Nilghiri Hills, India. 

 A. regalis Bens. Borneo. 



A. bajadera P/?-. Bengal. 



Japan. 

 China. 



China. 



China. 



Amazons. 



Helix quresita Desk. 

 H. filippina Heiide. 

 H. subsimilis Desk. 

 H. cicatricosa Miill. 

 Orthalicus regina Fer. 

 Columna flammea Marlyn. 



Prince Edward's Island. 

 Partula canalis Motiss. Samoa. 



P. rubescens Rve. Upolii. 



P. amabilis Pfr. Marquesas Islands. 



Amphidiomus sinensis Beits. Pegu. 



A. porcellanus Motiss. Java. 



I Admirably illust-ated by diagrams in J. \V. Taylor' .s Monog. of the Brit. L. and F. IT. 

 Moll., vol. I, pp. Ill, 112. 



