526 PROCEEDINGS OF THE ACADEMY OF [Nov., 



This form resembles P. a. suprastriatus closely, but differs by having 

 smooth post-embryonic whorls. It is also constantly black in color. 



Pachycheilus atratus suprastriatus n. subsp. 



The shell resembles P. atratus in shape and aperture. It is less 

 glossy, brownish black, dark brown or corneous-brown, the whorls 

 of the spire spirally striate, the striae sometimes persisting on the last 

 whorl below the suture. The earliest post-embryonic whorls are 

 acutely carinate, the carina continuing downward above the suture 

 as additional acute cords arise above it. On the third from the last 

 whorl, in a cotype, there are 5 equal acute striae! 



Length 3(H, diam. 15, aperture 13 mm.; G whorls remaining. 

 24, " 13, " 1H " 5 " 

 24^ mm. ; 1\ whorls remaining. 

 34, diam. 16 mm.; aperture 13 x 10 mm. 

 24, " 13 " " 10 x 7 " 



Yalles River at I\Iecos falls, and some rapids two miles west of 

 Mecos, State of San Luis Potosi, Mexico. 



The only species of Pachycheilus found in the vicinity of Mecos. 

 The young differ from those of atratus and ganinus in being carinate; 

 the early whorls of the spire enlarge more regularly, and the color is 

 a dull horn or light shade of brown without the polish of the young 

 atratus. 



Taken from the bed of the river in a moderate current, and sheltered 

 pools where there was no current. 



Mecos falls are a number of small falls and rapids where the Yalles 

 River comes from the mountains to the valley. Standing on the 

 railroad track and looking east and a little to the right, Yalles can be 

 seen as a spot in the valley, and still farther in the next range of moun- 

 tains is seen the rock face of the cut through which the railroad passes 

 and in which lies the village of El Abra. 



Paohyoheilus humerosus n. sp. PI. XXIII, figs. 21-2.3. 



The shell is ovate-turrited, solid, black with pale spiral bands on 

 the ridges, the cuticle smooth and dense. Spire acuminate when not 

 eroded, the earliest whorls (in young shells) clear brownish, first 5 

 whorls smooth and not very convex, then two spiral ridges appear, 

 rapidly becoming stronger, a third ridge appearing below the suture 

 about the 8th whorl, and sometimes others between the primary ridges. 

 A specimen 9 mm. long with S whorls has 7 spiral ridges on the last 

 whorl, each showing as a white band within the aperture. One 15 mm. 

 long with whorls has 7 such ridges and bands on the last whorl. The 



