230 PROCEEDINGS OF THE MALACOLOGICAL SOCIETr. 



ON THE DIVERGENT FORMS AT PRESElYT INCORPORATED IN 

 THE FAMILY MELANIIDJE. 



By J. E. S. MooEE. 



Read ^th December, 1898. 



Ijst his great work on the Morphology and Classification of the Proso- 

 branchiata, Bouvier ^ showed, after a study of several examples of true 

 Melaniidse and of the Cerithiidse, that it is impossible on purely 

 anatomical grounds to separate the one from the other, and he 

 has made it evident at the same time that within the Melaniidse 

 as a whole there are forms which in their morphological characters 

 are widely divergent from one another. Bouvier has described in 

 some detail the anatomical peculiarities of Melania amarula (Linn.), 

 Lamarck's type of the genus, M. costata, Quoy & G., M. filocarinata, 

 Montf., M. t'uherculata, Miill., and M. asperata, Lam. 



Through the courtesy of my friend Mr. Edgar Smith, I have been 

 able to examine a number of other Melanias, and we have con- 

 sequently now at our disposal a sufficient body of morphological facts 

 to enable us to discuss with profit the inter -relationships of these 

 forms. 



A large number of the genera and subgenera which are at present 

 included in the Melaniidse have never been examined anatomically, 

 but have been referred to this family with M. amarula (Linn.), solely 

 on the characters of their shells. 



On this account it will be found, in the succeeding survey, that 

 Bouvier's statements,^ firstly, that purely conchological determinations 

 are always to be regarded as more or less distinctly hypothetical, and 

 secondly, that " deux coquilles indentiques peuvent proteger des 

 ahimaux fort differents," are both quite true; and lastly, we shall 

 see that his conclusion, "la famille des Melaniides est une des plus 

 mal etablies dans tout le groupe des Prosobranches, elle est pour ainsi 

 dire basee sur les habitats des genres qui la composent," rather under- 

 than over-estimates the present unsatisfactory systematic aspect of 

 the group. 



Bouvier found that in M. amarula (Linn.) the nervous system is 

 constructed on a plan which is characteristic of a large group of 

 Prosobranchiata, including many families besides the Melaniidse. 

 In this form the cerebral ganglia are closely applied to each other, 

 while the pleural ganglia are equally closely applied to them 

 beneath, or rather immediately behind. On each side the great 

 pallial nerves have two separate roots, which anastomose in the body- 

 wall, and thereby give rise to what Bouvier has termed the dijaloneurous 



' Ann. Sci. Nat., ser. xvii, torn, iii (1887). 

 ' Tom. cit., p. 130. 



