I20 dall: groups of buumulus 



These are residents of the more arid zone, mostly found under rocks, 

 etc., and, like many of the other ground lovers, sometimes finely gran- 

 ulose. The shells are thin, slender, elevated, usually polished, but in 

 the variety pileahis the periostracum is raised into close low dull spiral 

 lamellae. Traces of these may be noted on some of the polished speci- 

 mens, and in all the apical whorls are sharply tranversely ribbed. 

 The peritreme is slightly expanded, the axis tubular, slender, and quite 

 simple. The distribution is rather scattered. 



Group of A^ snod grass: (Stemmodiscus n.). 

 N. snodgrassi Dall. 

 N. cucidliniis Dall. 

 N . galapaganus Dall. 



This group is confined to Hood, Gardner, Charles, and Barrington 

 Islands, and externally is not to be distinguished from Adenodia. 

 The internal structure is entirely different. The earlier part of the 

 axis is simple and tubular as in many other Galapagos species, but in 

 the first half of the last whorl, invisible from the aperture, a semi-cir- 

 cular disk-like flange projects (in the t3^pe) at right angles to the axis 

 into the lumen of the whorl and about half way toward the outer wall 

 of the whorl. This dwindles in front and behind into a short plaitlike 

 ridge on the axis which does not enter the penultimate whorl or reach 

 far enough forward to become visible from the aperture. This ar- 

 rangement recalls the lamina in Phenacotaxus umhilicatellus Pilsbr}% 

 of Peru, except that it is confined to the first half of the last whorl, 

 while in the Peru\'ian shell the lamina occupies part of three whorls 

 and has its major expansion in the penultimate whorl.- In A", cncullinus 

 the flange is shorter, rounder and less prominent than in A^ snodgrassi, 

 while in N. galapaganus it is thick and rounded. 



Group of A'^. aniastroides (Olinodia n.). 

 A'^. amasiroides Ancey. 

 N. nucitla Pfeifi"er. 

 A^ trogonius Dall. 



This group of small greenish-olive, ground -loving species is known 

 from Chatham, Charles, and Albemarle Islands. It must be rather 

 close to the presumed ancestral type. The axis is simple, slender and 

 twisted. 



Group of N. simrothi (Saeronia n.). 

 N. simrothi Reibisch. 

 N. toriuganus Dall. 

 A^. albemarlensis Dall. 



This is a group peculiar to Albemarle Island and its associate islets 



as far as known; ground loving, found under leaves and on low bushes, 



and in the grassy zone. They are small, short and stout, dull surfaced, 



more or less roughly wrinkled or corrugated, the adults having a 



- Smiths. Misc. Coll. 59: No. 14, p. 9, figs. 2. 1912. 



