HYATT: GENEALOGY OF ACHATINELLID^. 377 



is equi-umbilicated. While the asymmetrical is a secondary 

 modification occurring in more specialized organisms. In the 

 ontogeny, also, of asymmetrical forms we find that the young 

 are more loosely coiled than the adults. The umbilicus is 

 frequently open in the nepionic and neanic stages when in 

 later stages it is replaced by a columella or solid axis formed 

 by the contact of the inner side of the whorl. 



The Achatinellidce are wholly asymmetrical, but the most 

 primitive genus contains forms that are flat spirals having 

 open umbilici on the lower side. This leads in Kauai itself 

 into a series of more closely coiled and more asymmetrical 

 spires having solid columellae in adults ; and these into others, 

 of the genus Carelia, having elongated acute spires that can 

 be compared with those of highly modified shells like 

 Turritelld. 



Primitive Amastras, closely affiliated with the primitive 

 forms above described, that are not unlike a common Helix 

 in aspect, show traces of their derivation in their low spires 

 and so-called perforated columella. This perforated colu- 

 mella is in reality an umbilicus reduced to the dimensions 

 of a tube ; and even on Kauai this perforation disappears in 

 adults of one or two species. The fossil Amastras of Oahu 

 are apt to have perforated columellae; and on all of the 

 islands the most primitive forms exhibit more or less of this 

 character. In each series there are species and varieties that 

 can be distinguished by their more complete asymmetry. 

 This is shown in their more solid and twisted columella, 

 and in their more slender and elongated spires. There is 

 one entire series in Oahu which has all of the species of this 

 type, and one of them bears the appropriate name of 

 Amastra turritella. 



Turritelloidal shells appear repeatedly both less markedly 

 as variations and more decidedly as species on all of the 

 islands. 



All of these have a highly acute elongated spire quite dif- 

 ferent from that which is commonly seen in Amastras that 

 live exclusively on the ground, and on this account they have 

 been placed by Hartman in the genus Laminella. Laminella 



