870 PBOCEEDINaS OF THE NATIONAL MUSEUM. vol.xxii. 



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 Urw throughout, so that the surface is microscopically retic- 

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

 ei)idermis yellowish green or brownish, shining, ofteu 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, granularly striate. 



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

 Z7mo, not united posteriorly; branchiae large, equal in size. (Troschel.) 



Subgenus PEISODON Schumacher, 1817. 

 (Type, Mya syrmatophora Menschen.) 

 Characters as in the genus. 



tPRISODON SYRMATOPHORUS Meuschen in Gronovius. 



* Triquetra 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, 

 Concli. Sam., Ill, 1890, p. 189. 



* Margaron (Triquetra) subviridis Lea, Syn., 1852, p. 17 ; 1870, p. 25. 



* Mya syrmatopliora Meuschen in Gronovius, Zooph., 1781, pi. xviii, figs. 1, 2.2 — 



*Gmelin, Syst. Nat., 1788, No. 3222.— * Wood, Gen. Couch., I, 1815, p. 110.— 

 *DiLLWYN, Cat., 1, 1817, p. 54.— * Wood, Ind. Test., 182.5, p. 12, pi. ii, fig. 366. 

 "Hyria syrmatophora Sowekby, Rec. and Foss. Shells, XVI, 1823, fig. 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. 1, 1847, p.271.—* Wood, Ind. Test, rev., 1856, p. 17,pl. ii, flg.36.— *Hupe, 

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

 1869, pi. V, fig. 2.—* PiETEL, Conch. Sam., Ill, 1890, p. 189. 



* Unio syrmatoplwra Deshayes, Tr. Elem., II, 1853, p. 219, pi. xxix, figs. 10, 11. 



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



" ? Paxyodon ponderosus Schumacher, Ess. Nouv. Syst., 1817, p. 140, pi. xi, fig. 3. 

 ** Hyria avicularls var. b. Lamarck, An. sans 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^tel, Conch. Sam., Ill, 1890, 

 p. 189. 



* Hyria syrmatophora Kuster, Conch. Cab. Unio, 1856, p. 141, pi. xli, fig. 4. 



Cxuiana. 



' 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. 



