576 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.xxii. 



* Symphynota tenuissima Lea, Tr. Am. Phil. Soc, III, 1829, p. 453, pi. xi, fig. 



21; *Obs. 1, 1834, p. 67, pi. xi, fig. 21. 

 Symphynota tenuissima Short and Eaton, Transylvania Jl., 1831, p. 80. 



* Margarita (Unio) tenuissimus Lea, Syn., 1836, p. 38; 1838, p. 25. 



* Unio tenuissimus Hanley, Test. Moll., 1842, p. 206; * Biv. Shells, 1843, p. 206, 



pi. XX, fig. 42. — * Catlow and Eeeve, Couch. Nom., 1845, p. 64. — "H. and A. 

 Adams, Gen. Rec. Moll., II, 1857, p. 491.— * Sowerby, Conch. Icon., XVI, 1866, 

 pi. XLiv, fig. 240.—* B. H. Wright, Check List, 1888. 

 ^'Margaron (Unio) tenuissimus Lea, Sj^n., 1852, p. 38; 1870, p. 61. 



Upper Mississippi River drainage, south to the Tennessee River; 

 Buiialo, New York ; southern Michigan ; Souris River, Manitoba. 



(G-roup of Lampsilis scutulatus.) 



Shell rhombic elliptical, compressed, rather thin, with a high posterior 

 and a low anterior wing, with two jiosterior ridges; the valves often 

 exhibiting fine radiating plications on the posterior part; beaks com- 

 pressed, sometimes showing the nepionic shell, almost destitute of 

 sculpture, which, when present, consists of faint indications of two 

 rounded loops; epidermis rather dull, sometimes indistinctly rayed; 

 left valve with two pseudocardinals, the anterior a sharp, straight 

 ridge sloping obliquely downward and forward from a point just in 

 front of the beaks, the hinder curiously compressed and showing a 

 tendency to break into denticles; right valve with two sharp, ridge-like, 

 sloping pseudocardinals; laterals slender, compressed, straight or 

 wavy; nacre bluish white to pale violet; dorsal scars few; female shell 

 apparently slightly swollen at the posterior base; animal unknown. 



LAMPSILIS SCUTULATUS Morelet. 



* Unio scutulatus Morelet, Test. Noviss., I, 1849, p. 30. — * Fischer and Crosse, 



Miss. Sci., Pt. 7, II, 1894, p. 561, pi. lix, fig. 5; lxvii, fig. 6. 



Yucatan. 



LAMPSILIS PALUDOSUS Morelet. 



* Unio paludosus Morelet, Test. Noviss., I, 1849, p. 30 — * Fischer and Crosse, 



Miss. Sci., Pt. 7, II, 1849, p. 559, pi. lix, fig. 3. 



Yucatan. 



LAMPSILIS PLANIVALVIS Morelet. 



* Unio planivalvis Morelet, Test Noviss., II, 1851, p. 24. — * Fischer and Crosse, 

 Miss. Sci., Pt.7, II, 1894, p. 560, pi. lix, fig. 2.i 



Usumasinta River, Guatemala. 



t LAMPSILIS DELPHINULUS Morelet. 



^* Unio delphinulus Morelet, Teat. Noviss., I, 1849, p. 31. — * Hanley, Biv. Shells, 

 1856, p. 381, pi. xxiii, fig. 60.— Sowerby, Conch. Icon., XVI, 1866, pi. xliii, 

 fig, 237.— *B. H. Wright, Check List, 1888.— * PzETEl, Conch. Sara., Ill, 

 1890, p. 150.— * Fischer and Crosse, Miss. Sci., Pt. 7, II, 1894, p. 557, pi. 

 LXiii, figs. 2, 2a, 2b. 



* Margaron ( Unio) delphinulus Lea, Syn. 1870, p. 28. 



Guatemala. 



These three mav be mere variations of one thing. 



