1 31 2 • Diri.ODON 



almost black, with here and there fine, radiating grooves ex- 

 tending from the beaks. The greatest diameter is nearly in 

 the middle of the shell. Nacre very iridescent. In the right 

 valve are two lamellar cardinal teeth and a slender lateral ; in 

 the left valve the cardinal tooth has an auxiliary lamella above 

 it, separated by a groove. Above the lateral of the right valve, 

 towards the hinder part, is a slender lamella representing a 

 rudimentary second lateral. The beaks rise but little above 

 the narrow hinge. The muscular impressions are not very 

 deep, especially the posterior ones : the anterior retractor scar 

 is separate and distinctly marked. 



Length 49, height 2y, diam. 20 nmi." (von Ihering). 



Type locality, Lagoa, Alagadinha, Cioyaz, Brazil. 

 Dxplodon hartzvrighti von Ihering. Abb. Senck. Naturf. Ges., 



^2, iQio, p. 135, pi. 12, figs. Sa-b. 



The following are untigured and uncertain species. 



U)iio dcpressa d'ORBiGNV, Guer. Mag., 1835, p. 34. 

 Unio fokkcsi Dunker, Zeits. fiir Mai, IX, 1853, p. 54. 



Rio de la Plata, Brazil. According to von Ihering, this 

 equals U . zvlieatleyanns Lea. 

 Unio koseretsi Clessin, Mai. Bl., X, p. 172. 



River Guahyba, Brazil. 

 Unio macroptcrus Dunker, Zeits. fiir Mai., Ill, 1846, p. 109. 



Brazil. 

 ■ Unio paraguayanns von Martens, S. B. Ges. Nat. Fr., 1895, 



P- 34- 

 Unio .cealandicHs P.^tkl, C. Sam., Ill, 1890. p. 172. Said to 



be of Gray. Where? 

 Unio dantnoica d'ORP.iGNY. Where? 

 Tlnio guahybcc von Ihering. 

 Unio crthiopiformis von Ihering. 

 Unio bischoffi von Ihering. 

 Unio sebastancc von Ihering. 

 Unio sancta-poitlce von Ihering. 



I do not know where the last five species are described, and 

 'they prol)ably have never been published. 



