﻿4S2 SYMI'HYNOTA 



(loul)Iy-looi)C(l ridj^es ; the anterior ends of the ri(lj:;es coiiii 

 j^ated and subnodulous ; behind the ride^cs there are several 

 fine, radial, raised threads ; posterior rid^e low, double and end- 

 in<x behind at or near the base of the shell in a wide, feel)le 

 biaiiiiulation ; above this the posterior slope is obli(iuely trun- 

 cated; dorsal line nearly straicjht. joining^ the ix>sterior trun- 

 cation at an aui^^le ; basal line slij^htly curved or sometimes 

 str.'iii;ht; surface with uneven growth lines; epidermis usuallv 

 yellowish-green or i^reenish-yellow, somewhat rayed. rarel\' 

 ashy or brownish, suljshfning ; left valve with a com])ressed. A- 

 shaped tooth under the beak, which is reflexed, with a com- 

 pressed tooth in front of it, w'ith two or three, more or less 

 perfect, delicate laterals ; right valve with a compressed tooth 

 in front of the beak, the hinge line cut off under the beak and 

 one or two laterals; nacre bluish-white, buff or yellowish in 

 the cavities, dull, prismatic border wide. 



Length 104, height 60, diam. 30 mm. 



Length 105, height 56, diam. 30 mm. 



Length 82, height 46, diam. 27 mm. 



Ohio and St. Lawrence drainage areas; west to Nebraska, 

 north through eastern Iowa to Wisconsin ; Hudson River. 



Type locality, ( )hio ; Xorman's Kill, Albany, N. Y. 

 Symphvnota coinprcssa Lka, Tr. Am. Phil. Soc, 1829, p. 450, 



pi. xiT, fig. 22 ; Obs., L 1834, p. 64, pi. XII, fig. 22. — Simpson, 



vSyn., I goo, p. 662. 

 Complanaria compressa Conrad, Pr. Ac. X. Sci. Phila.. \'I, 



1853, p. 26 T. 

 Microcondykca comprcssa P^ETel, Conch. Sam.. ITT, 1890, p. 



Unio coiiiprcssiis Conrad. Monog., VIII, 1837, p. 71. pi. xi., 

 fig. I. — Hanlev. Biv. Shells, 1843, p. 174. pi. xx, fig. 39. — 

 De Kay, Zool. of N. Y., Ft. 5, 1843, p. 191, pi. xxi, fig. 245. 

 — KusTER, Conch. Cab. Unio, t86i, p. 198, pi. lxiv, figs. 3. 

 4. — SowERT?v, Conch. Icon., XVI, 1868, pi. lxi, fig. 303. 



Margarita (Unio) comprcssus Iaw. v'^yn.. 1836, p. ii; 1838. 

 P- 13- 



