870 PROCEEDINGS OF THE NATIONAL MUSEUM. 



hinder basal point to the end of the post dorsal wing generally 

 incurved: posterior slope having a radial row of plications, as in Cris- 

 taria; surface slightly concentrically sculptured and having delicate 

 radiating lira' throughout, so that the surface is microscopically retic- 

 ulated; beaks full, but not elevated, without sculpture as far as noticed ; 

 epidermis yellowish green or brownish, shining, often bronzy; hinge 

 narrow under the beaks, widening in front and behind; left valve with 

 two or more elongated compressed pseudocardinals which show a 

 tendency to break into denticles, and two laterals; right valve with 

 two or more similar pseudocardinals and a single lateral; laterals 

 vertically, grauularly striate. 



Animal with the labial palpi triangular, the hinder parts free as in 

 Unio, not united posteriorly; branchiae large, equal in size. (Troschel.) 



Subgenus PEISODON Schumacher, 1817. 

 (Type, My a syrmatophora Meuschen.) 

 Characters as in the genus. 



tPRISODON SYRMATOPHORUS Meuschen in Gronovius. 



* Triquelra subviridis KLEIN, Tent. M6th. Ost., 1753, p. 135, pi. ix, fig. 36.'* H. and 



A. ADAMS, Gen. Rec. Moll., II, 1857, p. 505; III, pi. cxx, figs. 1, la. *P.ETEL, 

 Conch. Sam., Ill, 1890, p. 189. 



* Margaron (Triquetra) siibviridis LEA, Syn., 1852, p. 17 ; 1870, p. 25. 



* Mya synnatophora MEUSCHEN in Gronovius, Zooph., 1781, pi. xviii, figs. 1, 2. : 



*GMELIN, Syst. Nat., 1788, No. 3222. * WOOD, Gen. Conch., I, 1815, p. 110. 

 *DILLWYN, Cat., 1, 1817, p. 54.* WOOD, Ind. Test., 1825, p. 12, pi. n, fig. 366. 

 *Hyria syrmatophora SOWERBY, Rec. and Foss. Shells, XVI, 1823, tig. d; * Conch. 

 Man., 1839, fig. 143. "REEVE, Conch. Syst., I, 1841, p. 120, pi. xc, fig. 1. 

 *HANLEY, Test. Moll., 1842, p. 214; *Biv. Shells, 1843, p. 214. *CATLOW 

 and REEVE, Conch. Man., 1845, p. 65. * TROSCHEL, Arch, fiir Nat., XIII, 

 Pt. I, 1847, p. 271. * WOOD, Ind. Test, rev., 1856, p. 17, pi. n, fig. 36.* HUI-E, 

 Moll. Nouv., Ill, 1857, p. 79, pi. xv, fig. 2. *SOWERBY, Conch. Icon., XVII, 

 1869, pi. v, fig. 2.* PJETEL, Conch. Sam., Ill, 1890, p. 189. 



* Unio syrmatophora DESK A YES, Tr. Eleiu., II, 1853, p. 219, pi. xxix, figs. 10, 11. 



* Margarita (Unio) syrmatophorus LEA, Syn., 1836, p. 11; 1838, p. 13. 



* f Paxyodon ponderosns SCHUMACHER, Ess. Nonv. Syst., 1817, p. 140, pi. xi, fig. 3. 



* Hyria avicularis var. b. LAMARCK, An. satis Vert., VI, 1819, p. 82. 



Guiana; Brazil. 



tPRISODON COMPLANATUS Hupe. 



* Hyria complanata HUPE, Moll. Nouv., Ill, 1857, p. 80, pi. xv, fig. 3. * SOWERBY, 



Conch. Icon., XVII, 1869, pi. iv, fig. 9. ' P.ETEL, Couch. Sam., Ill, 1890, 

 p. 189. 



* Hyria syrmatophora KUSTEK, Conch. Cah. Unio, 1856, p. 141, pi. xn, fig. 4. 



Guiana. 



1 Klein's species evidently equals the syrmatophora of Gronovius, but his name can 

 not be used, as he was not a binomial author. 



Gronovius used only generic names in the Zoophylaceum, and died while the 

 work was in progress. Meuschen finished it and figured the above species and 

 described it in the explanation of the plate. 



