1888.] NATURAL SCIENCES OF PHILADELPHIA. 19 



lines commence at the termination of the first one-and-a-half whorls 

 of the apex, which corresponds to their embryonic age. The apices 

 of some of the Amastra are coarsely plicate, in this respectresem- 

 bling Laminella. This is especially noticeable in the elongate spe- 

 cies, as A. magna, assimilis, biplicata, Hitchinsonii, turritella and some 

 others which have been classed Avith Laminella by Dr. Pfeifier ; in 

 others the plica of the apex are small Avrinkles, and in A. farcimen, 

 reticulata, tristis, elliptica, and some others, the apex is smooth and 

 rounded, forming a sub-group of Amastra. A more constant char- 

 acter is found in the species of Amastra being destitute of spiral 

 striae, differing in this respect from the ])orj)hyroid Achatinellse. 

 The Amastra being ground species and living beneath dead leaves 

 and other debris, when the shells are deprived of the animal and are 

 exposed to the atmosphere, the ejiidermis is more readily detached 

 than in other Achatinelke. 



"The facts relating to the geographical distribution of Achati- 

 nella, and the development of so large a number of species within 

 the limits of small areas, are very remarkable and interesting, 

 and have presented problems bearing or. the theories of evolu- 

 tion. Each island has its own peculiar species, and not only species^ 

 lout its own peculiar types, or groups of species, of similar form. 

 Again, on islands where there has been a full development of Acha- 

 tinella, each principal mountain ridge and valley has its own pecu- 

 liar species which are found nowhere else; the species of each ridge 

 or valley being often connected with those of the next — by intermediate 

 varieties. Another important fact observed in the distribution of the 

 Achatinella is. that on a mountain chain with many culminating 

 peaks, the tendency is to divergence of species, while on an indi- 

 vidual mass of mountains concentrating towards a single culminating 

 peak, the tendency is to a convergence of species." "The structure 

 of the Hawaian Islands is volcanic ; and in studying the distribution 

 of shells over them, it is important to note the relative ages of the 

 several islands. Geologically speaking, Kauai is the oldest ; next 

 in the series is Oahu ; then jNEaui with the adjoining islands of 

 Molokai and Lanai ; and last comes Hawaii, in the southern por- 

 tion of which volcanic fires are still raging." 



" Oahu. The development of Achatinella on this island, both as 

 regards number and variety of form and color, has been greater than 

 on any other island of the group. Unlike most of the other islands 

 which have individual mountain masses, Oalm has two true ranges 

 or chains of mountains, a longer and a shorter one, with many in- 



