524 PROCEEDINGS OF THE ACADEMY OF [Nov. , 



von Martens figured a specimen from the Berlin Museum, taken by 

 Ferdinand Deppe between 1824 and 1837. These examples were 

 labelled as from Lake Chapala, at the western edge of the Mexican 

 plateau, and draining into the Pacific. It seems unlikely that this 

 snail has any such range, and we are disposed to believe that some 

 mistake about the locality of Deppe's shells has crept in. They agree 

 fully in shape and sculpture with the Coy River examples, but, like 

 M. rabida Lea, are dead shells, of a reddish color. 



Pachycheilus pluristriatus longus n. subsp. PI. XXIII, figs. 11, 12. 



The shell is longer than pluristriatus, black, sometimes fading to 

 flesh color towards the apex, not glossy. The keel above the suture 

 is more prominent and the other spirals are fewer and unequal, part 

 of them being very weak, and they are black like the ground color. 

 The suture is deeply impressed; the base of the last whorl is smooth 

 or weakly sculptured. 



Length 37.3, diam. 14.3, aperture 13.5 mm. ; whorls 9^. 

 36, " 14.5, " 13.3 " " 12. 



Ganina River, there miles southwest of San Dieguito, San Luis 

 Potosi. 



Pachycheilus pluristriatus tamasopensis n. subsp. PI. XXIII, figs. 6-10. 



The shell is glossy, black, shaped like P. pluristriatus. Sculpture 

 weaker, the whole last whorl or its basal half being smooth, without 

 spiral cords, but generally a few spirals persist below the suture. 



Length 36^, diam. 17, aperture 14 mm. ; whorls 5^. 

 38' " 15, " 15 " " l\. 



34, " 13, " 14 " " 7i. 



Small stream north of the mill of the Tamasopo Sugar Co., San Luis 

 Potosi. 



Some small examples with the upper whorls eroded show no spirals 

 whatever, and may possibly belong to another species (pi. XXIII, 

 fig. 8). More perfect adult shells or the young stages must be examined. 

 Examples measure : 



Length 25, diam. 13, aperture 11.7 mm.; whorls 3. 

 " 26.5 " 15.2, " 11 " " 4J. 



Pachycheilus atratus n. sp. PI. XXIII, figs. 13-18. 



The shell is ovate-turrited, solid, covered with a very smooth, dense, 

 glossy brownish-black cuticle. The spire is somewhat acuminate; 

 early whorls smooth; intermediate whorls often showing a few weak 



