TAYLOR : VARIATION OF LIMN^A PEREGRA. 305 



Monst. decollatum Jeffreys. "Shell more or less eroded, spire truncate." 

 Brit. Conch., I., p. 106, 1862. 



■ Decollation, by which term we allude to the loss, usually 

 by erosion, of more or less of the apical whorls, has in many 

 species received distinctive name?, and the terms cariosa Gene, 

 corrostis von Gall., decollala Zgl., Jeffr., Anders., have been 

 applied to the specimens showing this phenomenon in Z. peregra. 

 Under the head of decollated forms we mny with almost perfect 

 safety comprise nearly all carious or eroded shells, for if erosion 

 or disintegration of the shell substance takes place at all, it is 

 practically certain to attack the upper whorls, as it is there the 

 protecting epidermis is thinnest and most delicate, and therefore 

 from time and other causes more liable to injurious influences. 

 Some specimens of this genus are at times so extensively eroded 

 that little or none of the epidermis is left intact. 



Specimens encrusted by various extraneous substances 

 have been from time to time and by various authors dignified 

 by special names: thus, the vars. opaca of Locard and Ziegler 

 are shells encrusted with a black or blackish deposit, but if the 

 deposit is blackish-brown or smoke-coloured they become the 

 var. fuUginosa Zgl. The varieties nigrita Gassies and nign'fiiis 

 Zgl. have also received their names from being similarly coated. 



The foregoing somewhat lengthy paper upon this species does 

 not by any means, even approximately, exhaust the material from 

 which much interesting matter could be derived. I have, how- 

 ever, dealt with the bulk of the forms in my own collection, and 

 trust that those conchologists who have given this group of shells 

 any amount of study will supplement, correct and complete as 

 far as they are able, the preliminary account I have given. The 

 whole subject of varieties and variation may be and is actually 

 viewed from so many different standpoints that it is hopeless to 

 expect all to agree as to the utility or even the desirability of 

 discriminating with precision the different forms which any given 



