UNIO 703 
-rounded and narrowed; muscle scars small, impressed; beak 
cavities moderately deep; nacre fine rose-color, thicker in front. 
The surface is ornamented with from one to five spines of 
various lengths in each valve, varying from one to twenty-five 
millimeters in length. They are either straight or crooked and 
though usually arranged in a radial row just in front of the 
posterior ridge they are sometimes scattered irregularly over 
this part of the shell. 
Length 102, height 60, diam. 33 mm. 
Length 95, height 50, diam. 40 mm. 
Type locality, Altamaha River. Georgia. 
Unio spinosus 1£A, Desc. of New Sp. Unio, 1836, colored figs. ; 
Pei, ell soc, VI, 1838, p: 57; plexviy fis. 50;‘Obs., IT, 
£838, p. 57; pl. xvi, fig.°50.— JAY, Cat., 1839; p. 113, pl. v, 
figs. I, 2.—Hantey, Biv. Shells, 1843, p. 182, pl. xx111, fig. 
56.—Kustrr, Conch. Cab. Unio, 1856, p. 167, pl. xix, fig. 
1.—CHENU, Ill. Conch., 1858, pl. xxur, figs. 6, 6a, 6b.—Sow- 
ERBY, Conch. Icon., XVI, 1866, pl. xix, fig. 261—SIMPsoNn, 
Syl LOGO). Pp: 730- 
Margarita (Unio) spinosus Lia, Syn., 1836, p. 17, colored 
plate; 1838, py 16: 
Margaron (Unio) spinosus Lasa, Syn., 1852, p. 23; 1870, p. 35. 
Canthyria spinosa Swanson, Tr. on Mal., 1840, pp. 276, 378. 
Unio spinosa Goonricn, Ill. Nat. Hist., II, 1859, p. 523, fig. 
Elliptio (?) spinosus ORTMANN, Ann. Car. Mus., VIII, 1912, 
p. 260. 
Probably this is the most remarkable member of the family 
Unionide. Dr. Lea has a magnificent series of 31 specimens 
ranging from young to old and exhibiting great variation. In 
one specimen the right valve is destitute of spines; in another 
there are no spines at all, but as it is somewhat eroded they 
may have been eaten away. In a young shell a spine is seen 
in each valve in the process of formation, being merely a short 
tubular development open at the outer ends and in front. The 
spines are compressed lengthwise, the growth lines on the 
upper side of them running across them; on the lower side 
it is curved sharply downward to a sort of median sulcus. No 
