266 MEMOIRS OF THE CARNEGIE MUSEUM. 



Laterals long, thin and narrow. Beak-cavity shallow. Dorsal muscle-scars in 

 beak-cavity. Anterior adductor-scars distinct and well impressed, those posterior 

 faint and indistinct. Nacre silvery white, highly iridescent posteriorly. 



Sexual differences present in the shell, but not always very striking. The 

 male shell has the posterior end more or less attenuated, narrower than the anterior 

 end, and the lower margin has a rather regular curve. In the female shell the 

 lower margin is a little expanded in the postbasal region, so that its middle part 

 is nearly straight, and its posterior part curves up more strongly. In consequence 

 of this, the posterior end of the shell is more broadly rounded, and more nearly 

 resembles the anterior end. There are cases, in which the female character is 

 very slightly developed, and others, where males do not show very well the posterior 

 tapering of the shell. As a rule, however, the sexes are rather easily distinguishable. 

 Female shells seem to be smaller on the average than male shells. 



L 



Size: 1. Edinburg, Cat. No. 61.3531 (probably &) 92 mm. 



2. New Galilee, Cat. No. 61.1797 (sex ?) 71 



3. New Galilee, Cat. No. 61.3265 (cT) 68 



4. Pulaski, Cat. No. 61.4830 (d^) 55 



5. New Galilee, Cat. No. 61.3265 ( 9 ) 49 



6. Waterford, Cat. No. 61.4096 ( 9 gravid) 43 



Soft parts (See Ortmann, 1912, p. 341, fig. 23). Glochidia (See Ortmann, 

 1912, p. 342). They are identical with those of the var. novi-eboraci according to 

 Surber (1912, PL 3, fig. 46). Surber gives the measurements: 0.240 X 0.300, 

 while I gave: 0.22 X 0.28 mm. 



Breeding season: The following records are at hand: Sept. 14, 1909; Sept. 

 18, 1917; and May 11, 1907; May 13, 1910; May 13, 1911; May 23, 1911; May 

 24, 1911; July 30, 1914. All my specimens had glochidia. Surber (1912, p. 7) 

 found glochidia in September, and Wilson & Clark (1912) report this species as 

 gravid (in Kankakee River) on July 28, and Aug. 3. All this speaks for a brady- 

 tictic form. 



Remarks: This is a shell well characterized by size, shape, and color. It can 

 not be easily confounded with any other Pennsylvanian species. However, young 

 specimens somewhat resemble E. fabalis, but are distinguishable at a glance by the 

 relatively thinner shell, and weaker hinge teeth. The extreme brilliancy of the 

 nacre in the posterior section of the sheU is also characteristic of this species. 

 The latter character distinguishes E. iris also from young Lampsilis luteola, which 

 resembles it to some extent. In addition L. luteola has more distinctly defined 



'" A giant, and apparently an exceptional case. 



