4 THE AMERICAN MIDLAND NATURALIST 
ventral margin. ‘The anterior adductor muscle scar is’ deeply 
excavated, longer than wide and strongly striated. The posterior 
adductor muscle scar is but lightly impressed, and in some specimens 
is highly iridescent. The pallial line is deeply impressed anteriorly 
but only slightly impressed posteriorly. This shell approaches 
closely to those of Unio luteclus and Unio ventricosus. It can be 
distinguished from U. ventricosus by its receding umbones, and it 
lacks the undulations that are so characteristic on the beaks of 
luteolus. : 
Length 17 Height 65 Diameter 22 
135 84 40 
122 72 36 
I51 86 48 
127 73 36 . 
~Lampsinis Recra (Lamarck). 
Unio recta Lamarck, An. sans Vert., VI, 1819, p. 74. 
Eurynia (Eurynia) recta Ortmann, Am. Car. Mus., VIII, 1912, p. 344, fig. 24. 
Unio rectus Conrad, Monog., III, 1836, p. 33, pl. XV. 
Lampsilis rectus,Smith, Bull. U. S. Fish Com., 1899, p. 290, pl. LX XVIII. 
Unio latissima Rafinesque, An. Gen. Sci. Phys. Brux. Pt. 13, V. 1820, p. 
OT Dl OOS 14S SSE 
Mya praelonga Eaton, Zool. Text-Book, 1826, p. 220. 
Unio leprosus Miles, Rep. Geol. Sur. Mich., 1861, p. 240. 
Observations and comparisons made on forty specimens in the 
museum at Notre Dame warrant the following descriptions and 
measurements. The shell is large, smooth and elongated; there 
is lateral compression and the shell is quite thick to very thick 
anteriorly. The epidermis is thick and blackish and obscurely 
rayed with numerous bands of green. These bands of color dis- 
appear in old specimens and are indistinct in some young ones. 
The cardinal teeth are double in both valves, those in the left 
valve are about equal in size. The anterior tooth in the right valve 
is so small as to be inconspicuous. The teeth generally are re- 
curved posteriorly, stout, triangular and: serrated. The lateral 
teeth are long, straight, lamelliform, elevated and crenulated. 
The anterior adductor muscle-scar is wing shaped, longer than 
wide and very deeply excavated. The posterior adductor muscle 
scar is rounded, slightly impressed and concentrically striated. 
The pallial line is deeply impressed anteriorly, crenulated, but only 
slightly impressed posteriorly. ‘The cavity of the beaks is very 
shallow. The nacre is variable showing all shades from pure white 
to a dark purple. 
