304 TAYLOR : VARIATION' OF LIMN'^A PF:REGRA. 



is encrusted with a dark extraneous deposit. I have occasion- 

 ally observed that this pearly appearance of the interior is very 

 noticeable shortly after the death of the animal, when the shell 

 has remained exposed. 



Monst. sinistrorsum Jeffreys. Shell with the spire sinistral or reversed. 



I have not thought it necessary to give a figure of this 

 form, as the only difference from the ordinary specimens is the 

 reversal of the direction of convolution. Dr. Baudon has 

 applied the term sinistra and Dr. Jeffreys that of sinistrorsa to 

 specimens exhibiting this peculiarity. The latter author gives 

 Limnaus luieatus Bean as a synonym without comment, but it 

 should be remarked that Bean included both dextral and 

 sinistral forms under that name, and had chiefly in view the 

 remarkably strong spiral ridging as the special peculiarity of his 

 variety, which peculiarity was shared alike by the normal and 

 the sinistrally coiled specimens. 



The example in my collection was obtained from a pond at 

 Tooting, by Mr. S. C. Cockerell, who kindly gave it to me. 



Monst. scalariforme Jeffreys. Shell with whorls more or less disjointed, 

 suture consequently very deep. 



This variety or monstrosity, which is characterized primarily 

 by its deep sutures, has also received the name of scalaiis from 

 A. Braun, and snbscalaris from Dr. Baudon, and may really be 

 considered as an accidental modification, which may be, and 

 probably is, often caused by the interposition of a solid 

 particle between shell and mantle, near the sutural line, compell- 

 ing a widening of the sutural groove, which is often continued 

 to the completion of growth. Such peculiarities acquired during 

 life are probably not perpetuated in the offspring, but disappear 

 with the death of the particular individual or individuals 

 affected, differing thus from deformities or malformations 

 dating back to the embryonic stage, which may be trans- 

 missible to succeeding generations, 



J.C., vi., Jan., 1S91, 



