JOURNAL OF CONCHOLOGY. 327 



mollusca discovered in actual transit from one locality to 

 another by the active aid of other organisms, some of the more 

 interesting methods being carefully figured. Many striking 

 cases of the more usual and better known methods of dispersal 

 are here discussed in detail. 



The fifth chapter demonstrates the vitality of mollusca, 

 and gives many recorded examples of their remarkable tenacity 

 of life, and of their retention of vitality when submerged in 

 salt water for a length of time sufficient to secure for them an 

 extended distribution under certain favourable circumstances. 



The eighth and ninth chapters deal exclusively with the 

 dispersal of the mollusca by voluntary or involuntary human 

 agency, and in chapter nine is enumerated some of the species 

 introduced into the British list owing to the discovery of speci- 

 mens on British soil, which had doubtless been introduced into 

 this country by some of the varied means here discussed. 



The volume is altogether of especial interest to British 

 Conchologists, as many of the author's most interesting facts, 

 illustrations, and conclusions are derived from observations on 

 British species. 



Abnormal Clausilia perversa. — Mr. W. Nelson has 

 recently shown me a most curious abnormal specimen of this 

 species found by him at Cooper's Hill, Gloucestershire. The 

 shell has evidently been damaged after attaining its full growth 

 and after roughly repairing the injury, has recommenced to grow 

 as a free tube for a length of six or seven millimetres, exactly 

 simulating the Cylindrellce in this particular. This abnormal 

 growth is entirely deficient of epidermis and seems to be formed, 

 entirely by the visceral mantle, bearing out the statement that the 

 glands of collar atrophy on the shell attaining the normal full 

 growth. It is somewhat remarkable that Mr. Nelson has found 

 two specimens oi Helix nenioralis in the same district, exhibiting 

 a similar character. — Jno. W. Taylor, December, 1893. 



