80 J. D. MACDONALD ON THE CLASSIFICATION OF THE GASTEROPODA. 



type of a separate family, with some more truly marine examples of which I am well 

 acquainted. Many Triincatellce live far inland, exhibiting a terrestrial habit as obviously 

 as any of the operculate Pulmonifera ; and their anatomical characters are well worthy of 

 a rigid comparison with those of Acicula. 



The FateUklo} exhibit many points of affinity to Fissurella, Nerita, and the series to 

 which they belong. Several members of the family manifest a tendency to deviate from 

 the typical species, in their dental formula in particular ; and indeed the whole lingual 

 armature in Fatella appears but to represent the rachidian area of Turbo or Nerita, — the 

 pleural teeth being suppressed, as in the mooted cases of Elysia, Eolis, &c., noticed in 

 the first part of the paper. 



The affinity here advocated is still further suggested by the peculiar sculpturing, 

 olivaceous colouring, and nacreous lining of the shell, in some species of Acmma. 



The Fatellidce and DentcdiidcB have a broad upper-lip mandible, and their ear-sacs con- 

 tain otoconia, but the resemblance ceases here ; while on the other hand in the Chitonidce 

 no upper-lip mandible exists, and I have never been able to detect either visual or audi- 

 tory organs. I must give up the attempt to class the two latter families ; but I think that 

 the Fatellidce may be placed provisionally at least as an appendix to the Fissurellidce. 



I have no desire to repeat former observations, and therefore refrain from any further 

 comment on the particular families contained in the Table. I can only say that I have 

 endeavoiued as much as possible to make the order of their arrangement in strict accord- 

 ance with their anatomical relations. With all its imperfections, therefore, the scheme 

 is submitted to the judgment of the zoologist, purporting to be merely a help to the 

 attainment of a precise conception of the natural affinities of Gasteropoda. 



