PEOCEEDINGS OF THE NATIONAL MUSEUM. 



strongly arclied, curved behind and incurved in front of the beaks; the 

 lower pseudocardinal in the right valve largest, often much split up 

 into denticles, pseudocardinals of the left valve variable, dentellate; 

 two lower anterior scars deep, united, the upper very deep, separate. 

 Animal unknown. 



Section CYCLOMYA Simpson, 1900. 



(Type, Unio funehralin Lea.) » 



fDIPLODON GRATUS Lea. 



*Unio grains Lea, Pr. Ac. N. Sci. Phila., IV, 1860, p. 91; * Jl. Ac. N. Sei. Pliila,, 

 V, 1863, p. 382, pLxLiii, fig. 290; " Obs., X, 1863,pl. xliii, fig. 290.— "SowereTy, 

 Conch. Icon., XVI, 1868, pi. lxxxiv, fig. 444.— *P.etel, Conch. Sam., Ill, 

 1890, p. 154. 



''Margaron ( Unio) gratus Lea, Syu., 1870, p. 56. 



Uruguay Eiver, South America. 



tDIPLODON PATELLOIDES Lea. 



*Unioimtelloide8'L-EA, Pr. Ac. N. Sci. Pliila., IV, 1860, p. 89; *J1. Ac. N. Sci. 



Phila., V, 1863, p. 383, pi. xliii, fig. 291; *0b8.,'X, 1863, p. 19, pi. xliii, 



fig. 291. 

 '^Margaron ( li^nio) patelloideir'L'KA, Syu., 1870, p. 56. 



Amazon Kiver, 



fDIPLODON PER.^FORMIS Lea. 



*Unio perwformis Lea, Pr. Ac. N. Sci. Phila., IV, 1860, p. 90; *J]. Ac. N. Sci. 



Phila., V, 1863, p. 384, pi. xliii, fig. 292; ^Obs., X, 1863, p. 20, pi. xliil fig. 



292.—* SOWERBY, Conch. Icon., XVI, 1868, pi. lxxxiv, fig. 443.— "P.etel, 



Conch. Sam., Ill, 1890, p. 163. 

 *Margaron {Unio) peroeformis Lea, Syn., 1870, p. 55. 



Uruguay Eiver, South America. 



tDIPLODON FONTAINIANUS d'Orbigny. 



* Unio fontainiana d'Orbigny, Guer. Mag., 1835, p. 36. 



* Unio fontainianus Hanley, Biv. Shells, 1856, p. 384, pi. xxi, fig. 27.— * Sowerby, 



Conch. Icon., XVI, 1868, pl.LXXXvii, fig.466.— ' Petel, Couch. Sam., Ill, 

 1890, p. 153.—* VON IHERING, Arch, fiir Nat., 1893, p. 90. 



*Margaron ( Unio) fontainianus Lea, Syn., 1870, p. 56. 



^ Unio fontaineana d'Okbjgny, Voy. Am. Mer.,1843, p. 60.5, pi. lxix, figs. 6, 7. — 

 *HuPE, Anim. Nouv., 1857, p. 82. 



Parana Eiver, southern Brazil. 



tDIPLODON ROTUNDUS Wagner. 



*Unio rotundus Wagner,' Test. Fluv. Bras., 1827, p. 34, pi. xxv, figs. 3, 4. — 

 *MoRiCAND, Mem. His. Soc. Gen., 1838, p. 49, pl.iv, figs. 12-14.— * Kuster, 

 Conch. Cab. Unio, 1856, p. 160, pi. xlvi, figs. 1, 2. — * Sowkrby, Conch. Icon., 

 XVI, 1868, pi. Lxxii, fig. 369.— P^TEL, Conch. Sam., Ill, 1890, p. 166. 



* Margaron ( Unio) rotundus Lea, Syn., 1870, p. 56. 



Brazil. 



^ Diplodon rotundum Spix in explanation of plate. 



