428 PROCEEDINGS OF THE ACADEMY OF [1896. 



In the recent revision" by Prof. H. A. Pilsbry of the genus Buli- 

 mulus Leach, the subgenus Bulimulus s. s. is defined as having the 

 apex irregularly wriukled or with the wrinkles broken into granules 

 or dislocated, while the subgenus Orthotomium has regular vertical 

 riblets. Ncesiotus is referred to the former. The South American 

 Bostryx has the apex smooth aud slightly swollen, not fuuiculate. 



An examination of the entire series of Ncesiotus in the National 

 Museum shows that the apex is nearer to that of Orthotomium than 

 to that of Bulimulus s. s. It is characterized invariably by vertical 

 riblets sometimes strong and with subequal furrowed interspaces; 

 sometimes distant with wider, flat interspaces, and sometimes ex- 

 tremely delicate and fine ; but, except when worn, always unbroken 

 and regular and with extremely fine spiral striae visible in a good 

 light, between the riblets. The apex always has a dimple or funicle 

 over the axis, but the upper margin of this is rounded, never keeled 

 as in some species of Orthotomium. This is an important point, as 

 it indicates the origin of the Ncesioti from the more northern stock, 

 or from the same source as the more northern stock. 



It often happens, especially among those species which have the 

 riblets low and fine, that they are broken by wear on the periphery 

 of the nepionic whorls, thus suggesting the Bulimulus type ; or even 

 that they may be entirely removed, while the polished surface shows 

 no traces of erosion. But in young, fresh specimens, they may 

 always be found unbroken and regular, except in the case of rare 

 abnormal individuals. Of the latter, I have come across only one 

 or two in all my series of several hundreds of specimens. 

 Bulimulus (Naesiotus) achatellinus Forbes. Plate XVII, figure 13. 



Btdimidiis achatellinus Fbs., P. Z. S., 1850, p. 56, pi. IX, figs. 5 a-b. 



Btdinmlus achaiinellmus Pfr., Mon. Hel. viv.. Ill, p. 429, 1853; Kiister, in 

 Chemn. Conch. Cab. ed. ii, Bulimus, No. 112, pi. 31, figs. 19-20. Pfr. Mon., 

 IV, p. 492, 1859. 



Bulimus {RAaphiellus) achatinellinus Pfr., Vers, in Malak. Bliitt., II, p. 160, 

 1855. 



Bulimulus [Oniphalostyla) achaiinellus H. & A. Ads., Gen. Kec. Moll., II, p. 

 161, 1855; Wimmer, Sitz. Akad. Wiss. Wien., Ixxx, p. 43, 1879. 



Buliminus [Rhaphielhis\ achatinellinus Martens, in Albeis, Heliceen, ed. ii, 

 p. 238, 1860. Reibisch, I'sis, 1892. p. 15, t. ii, fig. 8. 



Bulimma [Rhap/iielhts) achatinellitia Pfr., Nom. Hel viv., p. 300, 1881. 



Bulitnulus [Rhaphiellus) nchatinellinus Stearns, Proc. U. S. Nat. Mus., XVI, 

 p. 428, 1893. 



Habitat. Upper levels of Chatham Island on trees and bushes, 

 Kellett, Wolf and Baur; Hood Island, Habel, fi^de Wimmer. 



■ » Nautilus, IX, No. 10, p. 114, 1896. 



