BULIMULUS-NAESIOTUS. 95 



mitted. I have not hesitated to quote his observations both on the 

 general aspect of the fauna and on nearly all the species, as they 

 seem worthy of all confidence, and were based upon a mass of ma- 

 terial greater than any former malacologist has studied. 



No definition can be made which would cover all forms of Ncesio- 

 tus and exclude parallel species of similar contour from other regions. 

 The group is, however, a natural one, the species having doubtless a 

 common ancestry. The sculpture of the nepionic shell indicates 

 that the Galapagos group arose from the division of Bulimulus now 

 distributed over northern Mexico and Lower California, with a few 

 forms in eastern South America. It is not allied to the groups now 

 characteristic of Colombia, Equador, Peru and Chili. 



The anatomical details offer no characters by which the Gala- 

 pagos species may be differentiated from many of the Bulimuli of 

 the mainland. As Dall writes : " The utmost that can be said is 

 that Ncesiotus is a convenient term for the geographical group in- 

 habiting the Galapagos Islands, and, as such, we may retain it with- 

 out giving way to the delusion that it stands for anything more im- 

 portant." 



In NcBsiotus " the apex (pi. 24, fig. 35) is nearer to that of Ortho- 

 tomium than to that of Bulimulus s. s. It is characterized invaria- 

 bly by vertical riblets sometimes strong and with subequal furrowed 

 interspaces; sometimes distant with wider, flat interspaces, and 

 sometimes extremely 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 (pi. 24, fig. 36). 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. 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 Buli- 

 mulus type ; or even that they may be entirely removed, while the 

 polished surface shows no trace 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 speci- 

 mens " (DalV). 



" The nomenclature of this section has had serious vicissitudes, as 

 indicated by the above synonymy. The group was named Ncesiotus 

 by Albers who gave no derivation for it, though the sound of the 



