1896.] NATURAL SCIENCES OF PHILADELPHIA. 423 



C. What results in the shape of dynamic modifications may be 

 anticipated ? 



Answer. — The first result of room to spread, safety and plenty of 

 food, would be to release the species from the shackles of the en- 

 vironment from which they had been transplanted and to promote 

 general variability. 



(Ex. Wonderful variability of insular shell faunas, such as those 

 ■of Madeira, Galapagos and St. Helena Islands). 



Secondly, the particular features likely to indicate local dynamic 

 •influence under the assumed conditions would be : 



On the surface: wrinkling, corrugation or shagreening. 



(Ex. The great majority of land shells in such situations, as the 

 Selicidce in Madeira, the Bulimuli in the Galapagos, Succinea in 

 !inany islands, etc.). 



At the suture: plaiting or wrinkling more or less rhythmical. 



(Ex. B. achatellinus Forbes and B. nux Brod. of the Galapagos ; 

 •many Achatinella ; all the Pachyntis, etc.). 



At the vertex: loose coiling or dimpling of the nuclear coil. 



(Ex. Bulimuli of Lower California, Galapagos, Peru, St. Helena, 

 etc.). 



Of the axis : Exhibition of a tendency to irregularity, cork screw 

 twisting, or outward (internal to the tube of the axis, but external 

 to the tube of the shell) grooving in shells of elongated form, result- 

 ing in a tendency to form an angle or keel at the anterior edge of 

 the pillar within the aperture and an obscure channel at its extrem- 

 ity. 



(Ex. All the Pachijotis, many of the Ncesioti, Cleostyla, Pleuro- 

 pyrgus, Achatinella, etc.). 



Of the aperture: Thickening of the margin in connection with 

 hibernation, the formation of ill defined tubercles on the lips or par- 

 ies, irregularity of the margin with respect to the plane of incre- 

 iment, and a tendency to contraction at the full grown aperture dur- 

 ing or after hibernation. 



(Ex. Pachyotus, many Ncesioti, some Bulimuli of Lower Califor- 

 •nia, etc.). 



Of these characters some are more likely than others to be selected 

 as beneficial to the species, and these relate chiefly to general form 

 and coloration. In the matter of form the particular situs of the 

 species has a preponderating influence, small and slender shells be- 

 ing easier to manage in the narrow fissures under stones frequented 



