BULIMULUS-PLICOLUMNA. 151 



gin, continued in a rather strong callus across the parietal wall. 

 Columella with a long fold above and extending inward (fig. 74). 



Alt. 38, diam. 15, alt. of aperture 17 mill. 



Lower California : Cape St. Lucas (Xantus) ; San Jose del Cabo, 

 San Leonicio, etc., 100-3000 ft. alt. (Eisen) ; Sierra Laguna, 3000 

 ft. (Eisen, smooth var.) ; San Lazaro (Eisen). 



Bulimus imcendens W. G. B., Proc. Acad. N. S. Phila., 1861, p. 

 332, fig. PFR., Mai. Bl., 1864, p. 45 ; Monographia, vi, p. 149 ; viii, 

 p. 182. Bulimulus (Mesembrinus} inscendens BINN. & BLD., Land 

 and Freshwater Sh. N. A., p. 197, f. 343. CROSSE & FISCHER, 

 Moll. Mex., p. 544. pi. 21, f. 11, 11 a. Bulimulus (Leptobyrsus) in- 

 scendens DALL, Proc. U. S. Nat. Mus., xvi, 1893, p. 643, pi. 72, f. 6. 

 Bulimulus inscendens COOPER, Proc. Cal. Acad. Sci. (2), iii, p. 

 101 ; also pp. 208, 209 ; iv, p. 137, pi. 5, f. 4 (exclusive of subspecies 

 and varieties) ; v, p. 1 64. Mesembrinus inscendens TRYON, Amer. 

 Journ. Conch., iii, p. 170, pi. 14, f. 21. 



" The type specimens of this species show the very distinct gran- 

 ulation due to spiral strise, and have a nucleus like that of B. artem- 

 esia, obtusely keeled above. The pillar has a more or less distinct 

 fold, which, however, never becomes "laminar and is often feeble. 

 The spiral striation may be coarse, fine or absent. A smooth form, 

 that is, one in which there is no spiral striation or granulation of the 

 axially directed wrinkles, yet which has the form of the type, also 

 occurs. Both this and the type have large shells with flattish whorls 

 and a rather acutely conical spire." (Dalfy. 



Section Plicolumna J. G. Cooper. 



Plicolumna COOPER, Proc. Cal. Acad. Sci. (2), v, p. 164 (June, 

 1895). Pseudorhodea DALL, Nautilus, ix, p. 51 (Sept., 1895); 

 Proc. U. S. Nat. Mus., xviii, p. 5. 



Shell slender, small, with a nearly straight or gyrate and pervious 

 axis in the last whorl and a half, without internal lamina; aperture 

 less than a third the shell's length ; jaw as in Thysanophora. Type 

 Columna ramentosa, J. G. Cooper. 



Distribution, Lower California. 



The extreme attenuation of the shell is the main differential 

 feature of this group. It is to Orthotomium what Geoceras is to Lis- 

 soacme. 



