SOME NEW SOUTH AMERICAN LAND SHELLS 



By WILLIAM H. DALL 

 Curator, Division of Moli^usks, U. S. National Museum 



With One Plate 



Among some shells collected near the Atrato River, in the Sierra 

 Darien, by Mr. A, E. Heighway, and generously presented to the 

 Museum were Pleurodonte {Lahyrinthus) plicata Born, P. (L.) 

 sipimculata Forbes, and the following species which appears to be 

 very distinct from any other heretofore described. 



PLEURODONTE (LABYRINTHUS) TENACULUM, new species 



Plate XXXVII, Figures S, 6, lo, ii 



Shell dark purplish or chocolate brown, with a broad yellowish- 

 white band near the periphery of the whorls above and below ; whole 

 surface finely granulate, and covered with a thin brownish dehiscent 

 periostracum ; shell five-whorled, depressed, sharply carinate; upper 

 surface of the whorls (except the nucleus) flattened; the base mod- 

 erately convex, compressed near the periphery, rounding gently into 

 a deep funicular umbilicus ; nucleus pale, with obscurely vermiculate 



Fig. 64. — Diagram of aperture of Pleurodonte tenaculum showing armature. 



surface and a deep suture, which is subsequently closely appressed ; 

 incremental lines rather distinct and close set ; peristome white, the 

 whorl beneath the internal plications impressed externally ; the aper- 

 ture nearly parallel to the basal plane, thick, reflected, with no sulcus 

 at the umbilicus or carina, obscurely subquadrate ; parietal lamella 

 low, oblique, thin, strongly reflected outwardly, about five or six 

 millimeters long; basal lamellae two, the inner not longer than the 

 width of the reflection of the peristome, low, rounded, simple, nearlv 



361 



