12 PALUDINA INTEGRA. 



the original description, is a typographical 

 error. 



This may be a variety of P. decisa; but as 

 the characters appear to be constant, it may 

 stand as a species until a more extended exa- 

 mination of specimens can be made. Deshayes 

 has truly remarked, that specific distinctions 

 exist, not so much in the distinctness, as in the 

 permanency of the characters; and that it is 

 sometimes necessary to make extensive com- 

 parisons before just decisions can be made.* 



REFERENCE TO PLATE 3. 



Figs. 2 and 3 represent a very large individual; 1 is the 

 usual size and appearance; 4, a strongly marked variety; 

 5, the young; and , an opercle. 



* His words are "il faut, pour eviter une autre source 

 d'erreurs, avoir a sa disposition une collection tres con- 

 siderable par le nombre des especes et celui des individus 

 appartenant a chacune d'elles, la valeur d'un caractere 

 specifique residant plutot dans sa Constance, malgre sa 

 faiblesse, que dans sa grandeur, et cette Constance ne peut 

 etre constatee que par 1'examen d'un grand nombre d'indi- 

 vidus provenant de localites diverses." Lam. An. sans 

 Vert., torn. vii. p. 329. Anno 1836. 



