NO.1205. SYNOPSIS OF THE NAIADES— SIMPSON. 739 



XXIII, fig. 56. — *Catlow and Eeeve, Conch. Nom., 1845, p. 64.— * Conrad, 

 Pr. Ac.N. Sci. Phila., VI, 1853, p. 257.— * Kuster, Conch. Cab. Unio, 1856, p. 

 167, pi. XLix, fig. 1.— *Chenu, 111. Conch., 1858, pi. xxii, figs. 6, 6a, 6b.— 

 *SowERBY, Conch. Icon., XVI, 1866, pi. xlix, fig. 261.— *B. H. Wright, 

 Check List, 1888.— ^ P^tel, Conch. Sam., Ill, 1890, p. 168. 



"Margarita ( Unio) spinosus Lea, Syn., 1836, p. 17, colored plate; 1838, p. 16. 



*Margaron (Unio) spinosus Lea, Syn., 1852, p. 23; 1870, p. 35. 



*Canthyria spinosa Swainson, Tr. on Mai., 1840, pp. 276,378. — *Agassiz, Arch, 

 fur Nat., 1, 1852, p. 44. 



* Unio spinosa Goodrich, 111. Nat. Hist., II, 1859, p. 523, fig. 



Altamaha Eiver, Georgia. 



Section TJNIOMERITS Conrad, 1853. 

 (Type, Unio tetralasmus Say.) 



Shell trapezoid, with a rounded posterior ridge, and pointed or feebly 

 biangulate behind; beaks not prominent, sculptured with 10 to 15 

 curved, rather strong, concentric ridges, which sweep decidedly upward 

 behind, where they are drawn somewhat closely together; epidermis 

 generally rayless, often clothlike; pseudocardinals usually compressed; 

 laterals delicate, slightly curved; muscle scars large, shallow, nacre 

 generally lurid. 



Animal with the marsupium occupying the whole length of the outer 

 branchiae, pad-like; gills large, inner the larger, free nearly or quite the 

 length of the abdominal sac; mantle generally rather thick, thicker 

 and double on the edge. 



tUNIO TETRALASMUS Say. 



* Unio tetralasmus Say, Am. Conch., Ill, 1830, pi. xxiii.i — *Ferussac, Guer. Mag., 



1835, p. 26.— * Desha YES, An. sans. Vert., 2d ed., VI, 1835, p. 555; 3d 

 ed., II, 1839, p. 674.— *Hanley, Test. Moll., 1842, p. 198; *Biv. Shells, 

 1843, p. 198, pi. XXIII, fig. 49. — * Catlow and Reeve, Conch. Nom., 1845, p. 

 64.— *Chenu, Bib. Conch., 1st ser., Ill, 1845, p. 52, pi. x, figs. 1-3.— 

 * Conrad, Pr. Ac. N. Sci. Phila., VI, 1853, p. 258.— *H. and A. Adams, Gen. 

 Eec. Moll., II, 1857, p. 493.— * B. H. Wright, Check List, 1888.— * PiETEL, 

 Conch. Sam., Ill, 1890, p. 169. 



1 An abundant, widespread, and very A'^ariable species, and if there were no con- 

 necting links it would be easy to make a half dozen species out of it. The first 

 described is the Unio tetralasmus Say, an elongated, rather smooth, more or less shin- 

 ing form, of which excultus, jamesianus, parallelus, suhcroceus, and symmetricus seem 

 to be synonymous, varying a little in form, color, and smoothness. The variety camp- 

 todon of Say is quite rhomboid, and is a rather rough, dark shell, and U. symmetricus 

 is practically synonymous. Variety declivis is peculiarly drawn out at the post 

 basal point. Variety manuhius is a large, rather smooth form, rounded on the basal 

 line. All these are Southern and Southwestern forms. Variety sayi is a yellowish 

 shell, with very distinct rest marks, and has a more northern distribution than the 

 rest, but it absolutely blends into them. Ward sent a description of his U. sayi to 

 Tappan, who published it in the American Journal of Science and Arts under date of 

 1839. In Part XI of the Monography, dated November, 1838, Conrad describes Unio 

 sayanus (changed to sayi in his notes) and refers it to Ward in the American Journal 

 of Science and Arts of 1839. There is some mistake in these dates. In giving the 

 synonymy it is hard to tell in all cases just what authors have meant. 



