NO. 1205. SYNOPSIS OF THE NAIADES SIMPSON. 519 



tTRUNCILLA METASTRIATA Conrad. 



* Unio melastriutux COXKAD, MOIL, XII, 1840, p. 104, pi. LVII, fig. 2. 

 Black Warrior Kiver and Woodville, Alabama. 



(Group of Truncilla arca-formis.) 



Shell greatly inflated, with a sharp posterior ridge, and two lesser 

 ridges above it; inflation of the female flattened on its base. 



tTRUNCILLA ARC/EFORMIS Lea. 



* Unio arca-formin LEA, Tr. Am. Phil. Soc., IV, 1831, p. 116, pi. xvn, fig. 44; *Obs., I, 



1834, p. 126, pi. xvii, fig. 44. * ANTON, Yerz. der Conch., 1839, p. 14J 

 DESHAYES, Tr. Element, Conch., 1839, p. 18, pi. xxix, fig. 6. *HANLEY, Test. 

 Moll., 1842. p. 182; * Biv. Shells, 1843, p. 182, pi. xxn, fig. 40. "CATLOW and 

 REEVE, Conch. Nom., 1845, p. 55. *DESHAYES, Traito Element., II, 1853, pi. 

 xxiv, fig 6. *H. and A. ADAMS, Gen. Rec. Moll., II, 1857, p. 495. *CHENU, 

 111. Conch., 1858, pi. xn, figs. 3, 3a, 3&. *REEVE, Conch. Icon., XVI, 1864, pi. 

 xjv, fig. 57. 



* Margarita (Unio} arcwformis LEA, Syn., 1836, p. 18; 1838, p. 16. 

 Margaron ( Unio) arcaformis LEA, Syn., 1852, p. 23; 1870, p. 36. 



* Truncilla arca-formis AGASSI/, Arch, fiir Xaturg, I, 1852, p. 44. 



Unio nexus SAY, Transylvania .11., IV, 1831, p. 527; *SAY, Am. Conch., Pt. 6, 1834, 

 pi. Li. 2 *CONRAD, New F. "\V. Shells, 1834, p. 70. *FERUSSAC, Guer. Mag., 



1835, p. 28. ^CONRAD, Mouog., VIII, 1837, p. 68, pi. xxxvm, fig. 1. *KUSTER, 

 Conch. Cab. Unio, 1854, p. 69, pi. xvii, fig. 2. *CONRAD, Pr. Ac. N. Sci. Phila., 

 VI, 1853, p. 252. *PJ5TEL, Conch. Sam., Ill, 1890, p. 60. 



Tennessee and Cumberland river systems. 



Subgenus SCALENARIA (Rafinesque, 1820) Agassiz. 

 (Type, Unio aulcalus Lea.) 



Male shell having a wide, radiating, shallow depression in front of 

 the posterior ridge; that of the female having a small, rounded, well- 

 defined, radial post-basal swelling. Animal with marsupium occupy- 

 ing the greater part of the outer branchiffi; mantle enlarged below j 

 branchial opening, with few papilla 1 . 



(Group of Truncilla sulcata.) 



Shell elliptical, beaks high and well forward, male shell not radiately 

 striated posteriorly. 



'This may be T. triquetra. 



-According to Binney, Unio nexus was first published in December, 1831, (Bib. X. 

 Am. Couch., I, p. 266), and Scudder states that the fourth volume of the Transac- 

 tions, containing Lea's description of Unis arcwformis, was published at the latter 

 end of 1831, and acknowledged by correspondents as received that year (Bib. of pub- 

 lications of Lea, 1885, p. 3). As I am not able to say which has precedence, I prefer 

 retaining the well-known name of Lea rather than that of Say, which is less known. 



