674 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.xxii. 



Genus MARGARITAN A Schuniacher, 1817. 



(Type, Mya margaritifera Linun'iis. ) 



BajjMw Meuschen, Mns. Gevers, 1787, p. 472. 



Unto Retzius, part, Diss. Hist. Nov. Test. Gen., 1788, p. 16. 



Unto Oken, Lehrbuch der Nat., 1815, p. 236. 



Margariiana Schumacher, Essai Nouv. Syst., 1817, p. 137. 



Damalis (Leach manuscript) Gkav, Pr. Zool.Soc LoncL, 1847, j). 196. 



Baphia II. and A. Adams, Gen. Bee. Moll., II, 1857, p. 499.' 



Shell elongated, usually arcuate, rounded in front, almost lacking a 

 posterior ridge; beaks rather low, the sculpture consisting of a few 

 coarse, parallel ridges, which follow the growth lines; epidermis con- 

 centrically striate, brownish or blackish; hinge teeth generally imper- 

 fect or not fully developed ; two more or less i)erfect psendocardinals 

 in the left valve, and one iu the right, often reduced to meie tubercles; 

 behind these the hinge plate is narrow and rounded for some distance; 

 laterals short, usually imperfect or wholly wanting; cavity of the beaks 

 rather shallow; muscle scars large, those of the anterior roughened, 

 posterior elliptical; nacre generally more or less covered inside the pal- 

 leal line with small muscle scars. 



Animal with very long gills, inner wider in front, free for the greater 

 part of their length from the abdomiuiil sac, the two pairs united to their 

 posterior ends, which project backward for some distance unconnected 

 with the mantle; i)alpi very large, falcate, united half way posteriorly; 

 branchial opening having crowded, often arborescent papilhe arranged 

 in folds; anal opening smooth or crenulate; superanal opening not 

 closed below; marsupium occupying the entire outer gills.' Foot and 

 abdomen small; whole animal dark colored. 



tMARGARITANA MARGARITIFERA Linnaeus. 



Mya margaritifera Lister, Hist. Auim. Ang. App., 1685, pi. i, fig. 1. — Hist. 

 Conch., 1685, pi. cxlix, fig. 4.— * Linn.kus, Systema. Nat., lOtb ed., I, 

 1758, p. 671.— * Da Costa, Hist. Nat. Brit., 1778, p. 225, pi. xv, fig. 33.— 

 * Gmelin, Syst. Nat., 13th ed., 1792, p. 3219.'^—* Linn.eus, Fauna Suecica, 1761, 

 p. 2130.— Knorr, Vergn., IV, 1769, pi. xxv, fig. 2.— *M(iller, Vermes, 1774, 

 p. 210.— Pennant, Brit. Zool., IV, 1777, pi. xliii, fig. 18.— "Da Costa, Hist. 

 Nat. Brit., 1778, p. 225, pi. xv, fig. 3.— " Schroter, Fluss Conch., 1779, p. 168, 

 pi. IV, fig. 1.— *BoRN, Test. Mus. Vind.,1780, p. 21.—* Schroter^ Ein. Conch., 

 1783, II, p. 606.— * Donovan, Brit. Shells, III, 1801, pi. lxxiii.—* Montagu, 

 Test. Brit., 1803, p. 33.— *Turton, Brit. Fauna, 1807, p. 146.— "Maton and 



' The name Baphia Meuschen has precedence, but was never described ; it was applied 

 to a miscellaneous lot of bivalves, and is la the plural uumber. Retzius' first species 

 in Unio, the type of a section Avithout laterals, is the U. margaritifer, but in 1792 

 Brugniere in Choix de M6moires, I, p. 106, fully and carefully redefined the genus 

 Unio, restricting it to species with cardinal and lateral teeth. 



'^ According to Van Wahl. I have examined a great many animals taken at difierent 

 seasons, but have never seen one gravid. 



3 Refers to Conchylien Cabinet VI, pi. i, fig. 5, which is the form we know as Mar- 

 garitana margaritifera. 



