1276 DIPI^ODON 



point at the base of the shell ; anterior end slightly truncated 

 or round ; base line straight or faintly incurved ; surface with 

 feeble, uneven, concentric sculpture ; epidermis dark brown to 

 jet black, scarcely shining; left valve with one or two subcomr 

 pressed, rough, pseudocardinals and two laterals; right valve 

 with two pseudocardinals, the upper smaller, and one lateral ; 

 laterals with granular vertical stride ; anterior scars deep ; 

 there is a crescent shaped scar at the base of the pseudocar- 

 dinals ; posterior scars large ; nacre dirty bluish-white, darker 

 in the cavities of the valves, a little thicker in front. 



Length 88, height 40, diam. 27 mm. 



Patagonia. 

 Unio patago'tiica d'ORBiGNY, Guer. Mag., 1835, p. 37; Voy. 



Am. Mer., 1843, P- 610, pi. hxx, figs. 1-4. 

 Margarita (Unio) patagonicus Lea, Syn., 1838, p. 25. 

 Unio patagonicus Hani.ky. Biv. Shells, 1843, P- 208, pi. xxii, 



fig. 16. — Reeve, Conch. Icon., XVL 1865, pi. xxi, fig. 93. 

 Margaron (Unio) patagonicus Lea, Syn., 1852, p. 38; 1870, 



p. 61. 

 Diplodon patagGnicHs Simpson, Syn., 1900, p. 885. 



Not quite so decidedly pointed at the posterior base as 

 acittirostris ; the pseudocardinals are not so much split up and 

 the nacre is not so clean, yet probably the two run together. 



Diplodon acutirostris (Lea). 



Shell elongated, convex, very inecjuilateral ; with beaks prob- 

 ably somewhat full ; posterior ridge strong, curved upward in 

 the middle and ending in a point at the extreme base ; base 

 line incurved in front of the hinder point ; anterior end de- 

 cidedly truncated and ending in a right angle above ; surface 

 unevenly, concentrically sculptured, dirty olive, not shining ; 

 there is a large pseudocardinal in each valve split up into nu- 

 merous, rough, radial teeth ; one lateral in each valve, that of 

 the left somewhat double ; both are granular and show traces 

 of vertical striation ; anterior scars small and deep ; posterior 

 scars oblique ; nacre bluish-white, a little thicker in front. 



Length 80, height 40, diam. 24 mm. 



South America. 



