THE NAUTILUS. 



VOL. XXI. JULY, 1907. No. 3. 



DESCRIPTION OF A NEW MEXICAN PACHYCHEILUS. 



BY ANSON A. HINKLEY. 



PACHYCHEILUS VALLESENSIS n. sp. PI. 5, figs. 1-10. 



Shell conic, solid, smooth ; suture impressed ; aperture widely 

 ovate, circular at the base, obtusely angular above, purple within ; 

 whorls 7, convex ; on young and also well preserved specimens the 

 apical ones are slightly carinate or striate ; spire about half the 

 length of the shell. 



Operculum corneous, spiral, nucleus subcentral; when viewed from 

 above has a little resemblance to a small Planorbis. 



Length 32, cliam. 16 mm. 



Length 33, diam. 19 mm. 



Habitat. Valles river, Valles, State of San Luis Potosi, Mexico. 



" This species resembles short forms of P. /(evissimus, from which 

 it differs by the absence of fine spiral lines, the more heavily 

 calloused columellar lip, and the darker interior. No other Pachy- 

 cheilus has been found so far north." 1 



The species is named from the river in which it is the most plenti- 

 ful mollusk. Figure 1 may be considered the type, though its size 

 is above the average. There is often a flattening of the body whorl 

 and occasionally a constriction or shallow groove, as on some of the 

 Pleurocera. Mature specimens usually show 6 whorls ; when the 

 spire is well preserved, as in fig. 8 and fig. 9, there are 8. In young 

 specimens the aperture is angular below, see fig. 5. In mature 



1 Note from Dr. H. A. Pilsbry. The plate illustrating this species will ap- 

 pear in the next number. 



