212 AMERICAN JOURNAL 



Description. — Shell dextral, acutely conical, longitudinally 

 coarsely striate ; whorls 6, rounded, sometimes the last one 

 inflated ; suture simple, well impressed ; aperture ovate ; lip 

 acute, slightly thickened within ; columella rather long, with 

 a sub-central revolving plait ; often with an umbilicus. Color 

 dark corneous, outer and columellar lips margined externally 

 with white or yellowish-white. 



Long. *5, lat. "25 inch. 



Habitat. — Molokai, on the rocky sides of a Pali or precipice. 



Remarks. — Specimens of this species vary sufficiently in the 

 umbilical region, perhaps, to warrant their separation. Dr. 

 Pfeiffer, the highest possible authority, has founded his species 

 upon what I consider but a variety with a very open umbili- 

 cus, of which the figure furnishes a typical illustration. There 

 is, however, such a gradation between different specimens with 

 an open umbilicus and those which are closed, that I have 

 not found it possible to draw a line between the two extremes, 

 to determine where one ceases to be my petricola and becomes 

 the typical umbilicata of Dr. Pfeiffer. 



It may not, perhaps, be entirely uninteresting to Naturalists 

 to know the reason of the specific name given to this little 

 shell, which, to the author, recalls a scene of thrilling interest. 

 On the island of Molokai, as on some others of the Hawaian 

 group, may be found, in the mountain regions, deep gorges 

 inaccessible to man, with precipices of two thousand feet or 

 more, requiring to be scaled to reach the deep, dark, narrow 

 vale which some convulsion of nature has opened in the moun- 

 tain ridge. On such a mountain, so densely covered with 

 bushes four or five feet high, dead specimens of what was at 

 once detected as an unknown species were found. Desirous 

 of obtaining a supply, the writer determined upon making his 

 way over the bushes to an apparent opening a few rods distant. 

 In effecting this object, the branches of a friendly Tutui tree 

 were seized and used to drag the body forward. The opening 

 was reached, but, to my surprise, my body was poising itself 

 over a precipice, which, to my startled imagination, knew no 

 bottom. Resting on the yielding tops of the bushes, with no 

 support but the friendly Tutui branch, the position was one 

 that called for immediate and decided retrograde action, which 

 was, fortunately, effected in safety. On the rocks which formed 

 the upper rim of the precipice some twenty or more specimens 

 were obtained, and no shells in my cabinet have a stronger 

 claim on my affectionate regard than these plain Achatinellee, 

 which live above the clouds on the bushy cliff and along the 

 stony rim of this terrible precipice. 



