BULIMULUS. 127 



and were formerly brought together ; but a study of the apical 

 whorls shows that each of these groups is a special " parallel " modi- 

 fication of different Bulimulus stocks of ordinary form inhabiting each 

 of these regions, and it becomes clear that they are totally indepen- 

 dent and unrelated groups, with an origin and past history different 

 in each case. Again, an adequate study of specimens will, in my 

 opinion, convince conchologists that the similarity in appearance 

 between Chili-Peruvian and northern Mexican forms of the B. pro- 

 tens, erythrostomus, schiedeanus and montezuma groups, is not evi- 

 dence of close relationship but merely of similar environments. It 

 is unnecessary in this place to multiply instances of such parallelism 

 in the Bulimi. 



Primary divisions of Bulimulm. 



I. Apical whorls smooth, not wrinkled, costate or granular. Spe- 

 cies of Ecuador, Peru, Chili, Bolivia and Argentina. 

 II. Apical whorl* irregularly wrinkled subvertically, or with the 

 wrinkle* wavy, dislocated or variously broken into granules. 

 Species of Tropical America, West Indies and Galapagos Is. 

 III. Apical whorls with regular, straight vertical riblets. Species of 

 northern Mexico, Lower California and the southern United 

 States. 



The first of these groups consists of the single subgenus BOSTRYX, 

 including several "sections " of little systematic worth. 



The second contains several subgenera (see Nautilus ix. 114, and 

 the next volume of this work). 



The third forms the subgenus ORTHOTOMIUM, with two " sections," 

 Sonorina (n. n. for Leptobyrsus) and Plicolumna. 



I. Subgenus BOSTRYX Troschel, 1847. 



=Bostryx Trosch. -f- Peronceus Alb. -f- Ataxus Alb. -j- Pyrgiis Alb. 

 -f- Scutalus Alb. (larger part), -f- Temesa Ads. 



Shell varying from obese (or Helicoid) to slender and columnar 

 or subulate ; umbilicate or imperforate, more or less opaque and cal- 

 careous, sometimes corneous-streaked. Apical whorls smooth and 

 glossy, without sculpture of any kind. Aperture ovate or angular, 



