272 ANNUAL BECORD OF SCIENCE AND INDUSTRY. 



The family is quite peculiar to this group of islands, aud is 

 characterized by the columella having a spiral twist ; but 

 the singular fact is that most of the genera, and all the spe- 

 cies, are restricted, not only to a single island, but to very 

 small areas in the islands. In Oahu, an island 60 miles Ion 2 

 and 15 broad, there are about 185 species of Achatinellinse, 

 none of which are found on any other of the islands (with 

 scarcely an exception), and no species occupies a large pro- 

 portion even of this area. Nearly all are confined to the for- 

 est regions skirting two ranges of mountains, about 40 miles 

 in length by five or six in breadth; and no one species is 

 distributed over even one half of this small mountain range, 

 the greater number being restricted to areas from one to five 

 miles in length. The two ranges of mountains are inhabited 

 by species belonging to two different sections of the group. 

 From each side of the main range project mountain ridges, 

 w T hich separate deep valleys a mile or two in width ; and in 

 each of these valleys is a subordinate section, having its own 

 varieties, and in many instances its own species, which are 

 found nowhere else. The species of one genus found in the 

 same district are connected together by innumerable varie- 

 ties, presenting minute gradations of form and color, while 

 those found on different islands are not so completely linked 

 by intermediate forms. Granting the hypothesis that all 

 these various forms have sprung from a common ancestor by 

 a process of evolution, Mr. Gulick is quite unable to account 

 for the prevalence of particular forms in particular localities 

 by the theory of the " Survival of the Fittest," or any other 

 theory that has yet been propounded. 



PARASITES AND COMMENSALS OF FISH. 



A paper by Professor Van Beneden upon the fish of the 

 coast of Belgium, apj)earing in the memoirs of the Academy 

 of Science of Brussels, has an important bearing upon the 

 general economy of fishes, containing, as it does, very detail- 

 ed accounts of the food of the different species, and of the 

 animals, parasitic and otherwise, found in connection with 

 them. Professor Yan Beneden, in this paper, remarks that 

 all animals harbor a greater or less number of parasites, and 

 that there are very few that are more favored (or otherwise?) 

 in this respect than fish, which, as a general rule, especially 



