1909.J NATURAL SCIENCES OF PHILADELPHIA. 523 



Length 2(H, diam. 14^, aperture 13 x 11 mm., 4 whorls remaining. 

 17i ; " 13 , " lHx 9 " 4 " 



Moctezuma River at the ford south of Tampamolon, State of San 

 Luis Potosi; taken from rocks in shallow water where there was con- 

 siderable current. They were scarce. 



With some resemblance to P. pila, this species differs by its more 

 oval shape, the last whorl being less convex and larger, the aperture 

 less wide. P. pila has quite a different facies from the great expansion 

 of the last whorl. 



In some examples the spire is longer than in those selected as typical : 

 length 23, diam. 15, aperture 14 mm., whorls 6, the spire being perfect. 



Paohycheilus pluristriatus (Say). PI. XXIII, figs. 1-5. 



Melania pluristrktfa Say, New Harmon)' Dissem., Dec, 1831; Complete 



Writings, p. 140. 

 Pachycheilus pluristriatus Say, v. Martens, Biologia Central] Amer., Moll., 



p. 449, pi. 26, fig. 1. 

 Melania rubida Lea, Obs. Gen. Unio, etc., XI, p. 77, pi. 22, fig. 16. 

 Melania labiosa Wiegmann, in Berlin Mus. 



This species is solid, straightly conic, light slate or drab to nearly 

 black in color, glossy, usually with a yellowish band below the suture 

 and sculptured with numerous acute spiral cords narrower and much 

 lighter colored than their intervals, usually 10 to 15 on the last, 6 on 

 the penultimate whorl. The embryonic whorls are smooth, following 

 ones have a keel above the suture, and soon a thread above the keel; 

 additional threads soon appearing. The suture is either rather incon- 

 spicuous throughout or moderately impressed at the later whorls. 

 The last whorl is convex. Aperture purple-brown inside, ovate, 

 acutely angular above. Outer lip thin, retracted above. Columella 

 rather narrow. Parietal callus is rather heavy, or sometimes very 

 thick, white, brown at the edge. 



Length 37, diam. 17, aperture 15 mm.; whorls 8. 

 33, " 16, " 14 " " 71. 



35, " 15, " 13.3 " " 9. 



Coy River, San Luis Potosi, on a long water plant in the stream and 

 at the water's edge, quite abundant. 



The exact locality of Say's type of this species is not known. It 

 was taken by Mr. Maclure, who went to Mexico by the Tampico route, 

 and therefore may have obtained the shells from the Coy River or its 

 neighborhood. The examples taken by Mr. Hinkley agree fully 

 with Say's. The locality of M. rubida Lea was also unknown. Prof. 



