4 INTKODUCTION. 



more than the collector, who can glance at a plate where 

 the shell is figured. Some ludicrous results of attempting 

 to realize form from description may be seen in the draw- 

 ings of the old naturalist Gresner, who depicts elephants, 

 whales, besides other beings more fearful and wonderful 

 still, from the descriptions of people who had seen them, 

 or professed to have done so. 



Shells recently admitted into the British List. 



Within the last few yeurs several shells have made their 

 appearance in these islands. 



Some of these, whose introduction from foreign parts is 

 fairly established, have been admitted to rank with indi- 

 genous species. These are P. dilatatus, which came in 

 American cotton bales, and T. Maugei, which is shown to 

 have been introduced with continental plants sent to Bristol. 

 Both of these species have made themselves at home, and 

 are spreading. 



Others, known hitherto only as foreign, and whose 

 method of introduction is obscure, have been admitted by 

 some as British species. Among these are Clausilia parvula 

 and Helix villosa. 



Zonites glaler, Vertigo Lilljeborgii, and F. Moulinsiana, 

 though they had escaped notice till quite recently, can 

 hardly have been introduced by the ordinary methods, and 

 may fairly claim to be indigenous. 



A few long-established British species, whose introduc- 



