I3IO DIPl.ODON 



erodtd, in front of them at the anterior end of the dorsal mar- 

 gin is a small lunule 2-2.4 mm. in width. The ligament does 

 not reach to the end of the dorsal margin. Epidermis smooth, 

 blackish-brown, alternatiiig with black, polished, elevated, con- 

 centric zones, between which are the remnants of numerous, 

 lamellar, concentric growth-lines. The greatest diameter is at 

 about the centre of the total length and the anterior portion of 

 the shell towards the beaks is somewhat flattened. Nacre l)lu- 

 ish-white. thicker in front. The two cardinal teeth of the right 

 valve are almost lamellar but rather thick and straight, the 

 laterals are straight in the middle but oblique at both ends. 

 The cardinal tooth of the left valve is incurved on the lower 

 side. 



Length 55, height 2>t„ diam. 22 mm." (von Ihering). 



Type locality, Rio Panco, a tributary of the Rio Doce in 

 Espirito Santo, Brazil. 

 Diplodon panco von Jhering, Abb. Senck. Xaturf. Ges., 32, 



1910, p. 132, pi. 12, figs. 6a-h. 



"Other specimens vary somewhat in form. A low posterior 

 ridge is sometimes developed. The size of the lunule is also 

 a variable feature. The nacre in some shells is a pale yellow- 

 ish-red towards the ventral margin. The beak sculpture con- 

 sists of from \2 to 13 broad, rounded ridges, of which the 

 seventh and eighth meet at an acute, A'-sbaped angle." 



Diplodon garhei von Ihering. 



"Shell solid, thick-set. with widely separated beaks. The 

 specimen figured has the beaks greatly eroded and in front of 

 them a colossal, broad lunule 8 mm. in diameter. The anterior 

 end is very short, rather low and regularly rounded. The 

 hinder end is obliquely truncate, extending down in a decided, 

 rounded, post-basal point. \'entral margin concave in the 

 middle, but becoming convex as it approaches the posterior 

 point. The dorsal margin is bent sharj^ly downwards in front 

 of the beaks, behind them slightly convex. Epidermis l)lack- 

 ish-brown, sliim'ng. occasionally with squamose growth-lines 

 and iiere and there with fine, radial wrinkles. A moderate 



