ii8 daljl: groups of bulimulus 



ifomia Academy's Galapagos Expedition also indicate that iso- 

 lation was complete at least as early as Pliocene time, and present 

 an interesting admixture 'of west American and Indo- Pacific 

 types. 



By their superficial characters these shells are easily divided 

 into more or less closely related groups, some of which are re- 

 stricted in their range to particular islands or groups of islands. 

 Sectioning reveals that some of these are more emphatically char- 

 acterized by internal structure, the possession of internal laminae 

 not visible from the aperture and features of the columellar axis. 

 Of these groups at least fifteen are recognizable, and several of 

 them are so well marked as to have received names from the earlier 

 students. Only in recent years has the fauna been sufficiently 

 well known to enable the less emphatically characterized groups 

 to be recognized, and I believe no one hitherto has made a sys- 

 tematic study of the internal characters of the shells while the 

 first contribution to a knowledge of their anatomy was contained 

 in my monograph of 1896. A summary of the groups follows. 



Group of N. achatellinus Forbes (Rhaphiellus Pfeiffer, 1851). 



This species is strictly arboreal and appears to be rare. As with 

 the Achatinellas it exhibits more attractive coloration and variability 

 of pattern than the ground-loving species. The axis is tubular and 

 quite simple. 



Group of A^. nux Broderip (Xaesiotus Albers, 1850). 

 N. nux Broderip, with five varieties. 

 N. asperahis Albers (not of Reibisch). 

 N. bauri Dall. 

 These are chiefly arboreal, living on trees and bushes but descending 

 to shelter on the ground, in some cases, for hibernation. They are 

 confined to Charles and Chatham Islands and their associated islets. 

 The axis in general is slender, partly twisted and simple, the anterior 

 portion tubular. The aperture is unarmed, the surface dull and 

 wrinkled, the form stout, and the shell substance solid. 



Group of N. planospira (Granucis n.). 



A'', planospira Ancey. 

 N. rugulosus Sowerby. 

 N. invalidus Reibisch. 

 N. approximatus Dall. 



This group is confined to Charles Island so far as authentic records 

 go, except approximatus, which hails from Hood Island and differs 

 in surface from the others. These shells are more elevated and delicate 



