1909. NATURAL SCIENCES OF PHILADELPHIA. 525 



spiral cords below the suture and a weak angle at the shoulder. Last 

 whorl flattened below the very deep suture, elsewhere very convex 

 and smooth, though on some examples faint traces of very minute 

 spiral lines may be discerned. The aperture is rounded-oval or rounded- 

 ovate, somewhat livid and translucent within but generally with a 

 black band bordering the Up. It projects beyond the general outline 

 of the cone. Outer and basal margins of the peristome are thin, black, 

 and well rounded; inner margin straightened more or less, white 

 within, with a black or brown-black edge; 5 or 6 whorls remain in adult 

 shells, only the tips being eroded. 



Length 30, diam. 16 mm.; aperture 13 x 9 mm. 

 27, " 15i " " 13 xll " 



27, " 14 " " 12^x10 " 



Tamosopo River near Verastagu, San Luis Potosi, above and below 

 the "Natural Bridge" (pi. XXIII, figs. 13 to 15). 



While clearly related to P. hamerosus, this species is easily distin- 

 guished by its rounded whorls. A large quantity of each was taken. 

 The type lot consists of beautifully perfect, clean shells from above 

 the bridge. Those found below the bridge are not so clean. 



Specimens from a rill issuing from a cave on the mountain side above 

 Los Canoas are incrusted with a gray calcareous deposit so that adults 

 resemble pebbles, but when cleaned the shell within is found to be 

 almost or entirely perfect (pi. XXIII, figs. 16, 17, 18). Fig. 18 repre- 

 sents a cleaned specimen. They are smaller than the type lot, about 

 24 mm. long. 



A lot taken in the rill on the mountain above the "Natural Bridge" 

 consists of dwarf shells, adults measuring 19 to 21 mm. long. P. pila 

 in the same stream is even more dwarfed. 



Pachycheilus atratus ganinus n. subsp. PI. XXIII, figs. 19, 20. 



A race of P. atratus occurs in the Ganina River three miles southwest 

 of San Dieguito. The black shell is dull with the middle and lower 

 whorls of the spire ridged or coarsely striate spirally, usually with 5 to 8 

 striae on the penultimate whorl. Several of these spiral cords usually 

 continue on the last whorl below the suture. The upper whorls of the 

 spire are smooth and convex. The aperture is shaped as in P. atratus. 

 Fig. 19 represents a cleaned shell, fig. 20 one incrusted. 



Length 24, diam. 13, aperture 1H mm. 



There are some abnormally shortened shells, length 17, diam. 12, 

 aperture 10^ mm. The spire is generally covered with a hard cal- 

 careous crust, difficult to remove. P. pluristriatus longus occurs in the 

 same place. 



