HYATT: GENEALOGY OP ACHATINELLID^E. 373 



succession as clearly as if we could trace them from older 

 to newer and still newer strata in the field of geology. The 

 groups of genera so far determined in the family Achati- 

 nellidce are as follows: [Cyclamastra P. & V.] ; Kauaia 

 Sykes; Armiella Hyatt, Carelia and Amastra Adams; La- 

 minella Pfeiffer, Pe'rdicella Pease. I have reduced these to 

 the above list because in each case the group that appears 

 as a synonym is not separable from that in which it is in- 

 cluded, but is linked with some of its species by intermediate 

 gradations, often by hybrids. 



My definition of a genus in this family is a homogenetic 

 group which has been practically (not theoretically) traced 

 from variety to variety and species to species. I have on all 

 important points found myself in close accord with the Rev. 

 J. T. Gulick whose thorough studies of this group have placed 

 in my hands the means of doing this work, and whose labors 

 I hope some day to present with illustrations that will place 

 him among the great pioneers in the history of evolution. 

 A genus, in my opinion, is simply a genetic series which may 

 conveniently be separated from other closely related series 

 descended from the same common ancestors. 



According to Major Dutton's account, (Report of U. S. 

 Geol. Survey, 1882-83, Hawaiian Volcanoes), the Hawaiian 

 Islands lie between 154 30' and 160 30' W of Green- 

 wich, and 18 40' and 22 15' North latitude. They are 

 therefore near the northern border of the 'great equa- 

 torial current which flows westward from the western 

 coast of North America sometimes transporting materials 

 from those shores to the islands. The length of the en- 

 tire chain is from 350 to 400 statute miles and the distance 

 from San Francisco about 2000 miles. There are eight 

 islands and four barren rocks. Niihau, a small island, now 

 without any testaceous inhabitants, lies at the northwest end 

 of the series, and is followed by Kauai having only terrestrial 

 land shells, and no arboreal species, in spite of the fact as 

 stated by Baldwin that ' * Its extensive forests, luxuriant vege- 

 tation and moist climate render it peculiarly well adapted for 

 the abode of Achatinella." 



