NO. 1205. SYNOPSIS OF THE NAIADES— SIMPSON. 519 



tTRUNCILLA METASTRIATA Conrad. 

 * JJnio metastriatus C'oxkad, Mou., XII, 1840, p. 104, pi, Lvn, fig. 2. 

 Black Warrior River and Woodville, Alabama, 



(Group of Truncilla arcaformis.) 



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 arcaformis Lea, Tr. Am. Phil. Soc, IV, 1831, p. 116, pi. xvii, fig. 44; *0b8., I, 



1834, p. 126, pi. XVII, fig. 44.— * Anton, Verz. der Conch., 1839, p. 14.'— 

 Deshayes, Tr. Element, Conch., 1839, p. 18, pi. xxix, fig. 6. — ""Hanley, Test. 

 Moll., 1842, p. 182 ; ^^ Biv. Shells, 1843, p. 182, pi. xxii, fig. 40.— ^Catlow and 

 Eeeve, Conch. Nom., 1845, p. 55. — ""Deshayes, Traite Element., II, 1853, pi. 

 XXIV, fig 6. — *H. and A. Adams, Gen. Eec. Moll., II, 1857, p. 495. — *Chenu, 

 III. Conch., 1858, pi. xii, figs. 3, 3a, 3b. — *Reeve, Conch. Icon., XVI, 1864, pi. 

 XIV, fig. .57. 



^Margarita {JJnio) arowformis Lea, Syn., 1836, p. 18; 1838, p. 16. 

 Margaron (Unio) arcceformis Lea, Syn., 1852, p. 23; 1870, p. 36. 

 ^Truncilla arcceformis Agassiz, Arch, fiir Naturg, I, 1852, p. 44. 

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

 pi. LI.2— **CONRAD, New F. W. Shells, 1834, p. 70. — "Ferussac, Guer. Mag., 



1835, p. 28.— "Conrad, Monog., VIII, 1837, p. 68, pi. xxxviii, fig. 1.— *^Kuster, 

 Conch. Cab. Unio, 1854, p. 69, pi. xvii, fig. 2.— "'Conrad, Pr. Ac. N. Sci. Phila., 

 VI, 1853, p. 252.— *PiETEL, Couch. Sam., Ill, 1890, p. 60. 



Tennessee and Cumberland river systems. 



Subgenus SCALENAKIA (Rafinesque, 1820) Agassiz. 



(Type, Unio sulcafus 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 branchiie; mantle enlarged below; 

 branchial opening, with few papilla?. 



(Group of Truncilla sulcata.) 



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

 striated posteriorly. 



iThis may be T. triquetra. 



"According to Binney, Unio nexus was first published in December, 1831, (Bib. N. 

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

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

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

 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. 



