PHYSAD.E. 17 



Mr. Charlesworth remarks, in the first volume of his 

 Magazine of Natural History, that "Theory is often the 

 great incentive to observation, the main stimulus to exer- 

 tion, and the more widely those who are engaged in the 

 prosecution of the same object differ amongst themselves 

 as to the nature of their present conclusions, the greater, 

 perhaps, would be the reliance which we should feel dis- 

 posed to place in any points of common agreement that may 

 hereafter be attained." This being admitted, I would like 

 to see the Lamarckian hypothesis revived by some one 

 capable of doing it justice. I furnish in these pages an 

 additional intercalation, and consider that the Paludina 

 subcarinata might be viewed in this connection. In this 

 species we find a true Paludina, occasionally rounding its 

 aperture, throwing it off from the body whirl, and not only 

 assuming the physiognomy of Cyclostoma elegans, but 

 actually departing so far from the normal character of its 

 genus, as to construct a cyclostomoid opercle; that of the 

 young animal enlarging spirally. This, however, does not 

 continue; the animal, as a Paludina, is not endowed with 

 the elements necessary to produce the entire opercle of a 

 Cyclostoma, so that after continuing it to a certain point, 

 the layers become normal, or concentric, apparently indi- 

 cating the impossibility of a departure from its generic 

 type, beyond a certain limit. But instead of taking this 

 view of the shell in question, I regard it as one of the 



vulgar names has been carried so far, that some English 

 authors use the word pig! instead of hog or swine; Pro- 

 fessor Bell, however, has sufficient independence and re- 

 spect for the language, to avoid this suiscidal course, 

 i 3 



