ortmann: monograph of the naiades or Pennsylvania. 283 



Lampsilis luteola (Lamarck) (1819). 

 Lampsilis luteola (Lamarck) Simpson, 1914, p. 60. 



Plate XVII, figs. 1, 2. 

 Records from Pennsylvania : 



Clapp, 1895 (Allegheny Co.) 



Rhoads, 1899 (Ohio River, Coraopolis, Allegheny Co.; Beaver, River, Wampum, Lawrence Co.) 



Ortmann, 19096, p. 190, 202. 



Characters of the shell: Shell from medium size to rather large, moderately 

 thick. Outline subelliptical or subovate, moderately elongated, distinctly over 

 one-and-a-half times as long as high, but less than twice as long as high. Anterior 

 margin rounded. Lower margin more or less regularly curved. Upper margin 

 nearly straight, forming with the posterior margin a blunt angle, when young, or 

 passing gradually into it, when old. Posterior margin meeting the lower margin 

 in a very blunt angle, so that the posterior end of the shell is rather rounded off. 

 Beaks low, located in the anterior portion of the shell. Beak-sculpture (see Mar- 

 shall, 1890, fig. 3) fine, consisting of six to ten double-looped bars, with a distinct 

 re-entering angle in the middle. The posterior loop is slightly angular, and in- 

 distinct upon the posterior slope. Sometimes the first bar appears subconcentric. 

 Valves more or less swollen, rarely subcompressed, but flattened upon the sides. 

 Posterior ridge indistinct. 



Epidermis yellowish to light greenish, or light brownish, shining and smooth. 

 In old shells it is darker, but not blackish. Rays are generally present. They 

 are dark green to blackish, quite distinct, straight, narrow or broad, covering 

 more or less of the surface. Posterior slope often darker in color, and less shrnrng. 

 Growth-rests more or less distinct, but irregular. 



Hinge well-developed. Pseudocardinals two in left, one or two in right valve, 

 tooth-like, compressed or stumpy, crenulated, very variable. Interdentum absent. 

 Lateral teeth long, but rather thin, gently curved. Beak-cavity shallow. Dorsal 

 muscle-scars in beak-cavity. Adductor-scars distinct and well impressed, chiefly 

 the anterior one. Nacre milky-white, silvery, somewhat iridescent behind. 



Sexual differences very strongly marked. While the male shcU imiformlj' 

 tapers backward to the bluntly pointed end, having the lower margin rather evenly 

 curved, the female develops a considerable sweUing and expansion of the lower 

 margin in the postbasal region, so that the anterior part of the lower margin is 

 nearly straight (or even slightly concave), and the posterior section of it ascends 

 very suddenly to the posterior end. This produces a considerable widenmg of the 

 posterior end of the shell, which often appears truncated. In old females this 

 feature is so prominent, that the shell actually seems to be distorted. 



