﻿SVMl'IiYNOTA 489 



ridges ; ]:)osterior ridge well developed, sometimes partly dou- 

 ble ; posterior slope covered with strong, corrugated, radial 

 costations ; hinder half of the disk often slightly corrugated ; 

 grow^th lines strong and irregular ; epidermis yellowish-green, 

 green, tawny or brownish, often rayed, dull or subshining; 

 left valve with a strong. A -shaped reflexed tooth under the 

 beak, often with a low one in front of it ; right valve with an 

 irregular, subtriangular tooth in front of the beak, the hinge 

 plate cut away behind it ; laterals low and much blurred ; mus- 

 cle scars large, impressed, the anterior ones separate ; nacre 

 whitish or straw-colored. 



Length 146, height 91, diam. 40 mm. 



Length 124, height 57, diam. 30 mm. 



Length 96, height 63, diam. 29 mm. 



Mississippi drainage generally ; St. Lawrence basin ; Manito- 

 ba ; Hudson River ? ; Columbus, Mississippi ; Texas ? 



Type locality, Kentucky River. 

 Alasmidonta costata Rafinesouk, Ann. Gen. Sci. Brux., V, 



1820, p. 318, pi. Lxxxii, figs. 15, 16. 

 Alasmodonta costata Say, Am. Conch., VT, 1834. 

 Complanaria costata Conrad, Pr. Ac. N. Sci. Phila., VL 1853,, 



p. 261. 

 Symphynota costata Simpson, Syn.. iqoo, p. 665. 

 Alasmodonta rttgosa Barnes, Am. Jl. Sci., VL 1823, p. 278, 



pi. XIII, fig. 21. — Baker, Moll. Chicago, Pt. i, 1898, p. 57, 



pi. VII, figs. I, 2; VIII, figs. 3, 4. 

 Mya riigosa Eaton, Zool. Text-Book, 1826, p. 222. 

 Margarita (Margaritana) rugosa Lea, Syn., 1836, p. 44; 1838, 



p. 27. 

 Unio rugosa Hani.ey, Biv. Shells, 1843, p. 211, pi. xxi, fig. 8. 

 Alasmodon rugosa De Kay. Zool. N. Y., Pt. 5, 1843, P- 196. 



pi. xiv, fig. 226. 

 Complanaria rugosa Stimtson, Shells of N. Eng., 1851, p. 14. 

 Margaron (Margaritana) rugosa Lea, Syn., 1852, p. 42; 1870, 



p. 67. 

 Baphia rugosa H. and A. Adams, Gen. Rec. Moll., TL 1857, p. 



500. 



