1909.] NATURAL SCIENCES OF PHILADELPHIA. 527 



whorls then enlarge very rapidly, the suture deepens. On the penulti- 

 mate whorl of an adult there are about 5 spiral pale ridges, the lower 

 ones wider and lower. On the last whorl the ridges weaken, leaving 

 it smooth or nearly so, or they may persist below the suture and at the 

 base; the suture becomes very deep, the whorl below it horizontal, shoul- 

 dered, the shoulder bounded by a ridge or angle. The aperture is 

 rounded-ovate, blackish within but pale or banded in the throat; 

 outer and basal margins thin, black, broadly rounded; inner margin 

 more or less straightened, appressed or free and continuous, brown at 

 the edge, the callus white. 3^ to 6 whorls usually may be counted in 

 adult shells. 



Length 28, diam. 18, aperture 13^ x 10 mm. 

 27, " 17. " 14 xl2 " 



" 25, " ISi, " 14^x12 " 

 " 25, " 16£, " 14 xlOi " 



The operculum is ovate, with the nucleus about one-third across 

 from the columellar side and below the middle. 



Tamosopo River, near Verastagu, above and below the "Natural 

 Bridge." 



The light colored cords alternating with purple-black bands makes 

 it a conspicuous shell when seen in the water. While the general 

 shape is that of P. atratus, this species differs from that by its con- 

 spicuous sculpture. It is more allied to P. tristis, though very distinct. 



Pachycheilus monachus n. sp. PI. XXIV, figs. 21-25. 



The shell is solid, cylindric with conic spire, or turrite-conic, black. 

 The earliest whorls appear to be smooth; then sharp spiral cords much 

 narrower than their intervals appear, evenly spaced, and five on each 

 whorl; these disappear on the last two whorls, or one to three persist 

 only below the suture, where the whorl is more or less tumid or shoul- 

 dered. The spire is rather long and conic; suture deep; last whorl 

 convex or flattened laterally. The aperture is ovate, whitish inside, 

 black near the lip. Outer lip sharp and strongly arcuate. Columellar 

 lip more straightened, heavily white-calloused, usually brownish at 

 the edge. 



Length 32, diam. 14.3, aperture 13 mm. ; whorls remaining 8. 



28, " 13.3, " 12 " " " 4 



25£, " 14, " 12 " " " 4i 



Coy River, three miles south of Los Palmas. State of San Luis 

 Potosi, Mexico. 



The Coy River issues from a cave at the foot of the mountain below 



