404 PROCEEDINGS OF THE ACADEMY OF [1896. 



On the other hand, it is certain that the southeastern islands are 

 much better known than either of the other groups and that the area 

 and fertility of the central group are such that there is every reason 

 to suppose many more forms remain to be discovered there, perhaps 

 including some of those so far known only from the southeastern 

 islands. Prudence strongly urges that we know too little of the 

 mollusk fauna yet to intelligently discuss its inter-island distribution. 

 Taking the forms enumerated in the table showing the distribu- 

 tion of the species and omitting the Onchidium and species of A^iric- 

 tilidce and Siplwnariidce., all of which are denizens of the salt marshes 

 or beaches, we have forty-six, of which fifteen are found on more 

 than one island, five on more than two islands and three are 

 found without material change on four islands ; all of the latter are 

 found in both the central and southeastern groups of islands. One 

 of the species, and perhaps two, are probably common to the main- 

 land of South America as well as the Galapagos, and all of them 

 doubtless have been derived from the fauna of the Panamic and 

 South American region. 



The following table will show the distribution of the various spe- 

 cies among the several islands, as far as known, their presence being 

 indicated by an initial letter in the column devoted to the island 

 concerned. A, stands for the Albatross expedition ; B, for Dr. 

 Baur; C, for Hugh Cuming; D, for Darwin ; H, for Dr. Habel ; 

 K, for Kellett and Wood ; P, for the Peterel, Captain Cookson ; and 

 W, for Wolf as reported on by Reibisch, with some additions to his 

 printed list. The names are given in the left hand column, the col- 

 umns for the islands follow in the order of their distance from the 

 source of supply, approximately ; the last column sums up the num- 

 ber of specimens actually examined by the writer in preparing this 

 paper. 



One or two species are noted as new, which Herr Reibisch has 

 mentioned in his letters as now in his possession, in addition to 

 which are several Pupas which he regards as new, but has not in- 

 formed me to which islands they should be assigned. 



Habits and environment. — With the exception of Dr. Baur no one 

 seems to have noted very particularly the exact location of the spe- 

 cies collected, either with regard to altitude or situs. A few of 

 Wolf's species are so noted, but, as most of his specimens were dead, 

 their value in such a discussion is impaired. Cuming noted the situs 

 but neglected the altitude. The matter really needs the attention 



