﻿LAMPSTLIS 117 



The male shells are sometimes feebly biangulate behind, but 

 are more often rounded. I have only seen two female shells, 

 one of which seems adult and both are much smaller than the 

 shells of the males. They are rounded behind and have a 

 feebly developed marsupial swelling". 



Length (male) 68. height 33, diam. 22 mm. 



Length (female) 45, height 23, diam. 16 mm. 



Tennessee system. Beaver River, Pennsylvania. (?) 



Type locality, Holston River, Tenn. 

 Unio fatuus Lea, Pr. Am. Phil. Soc. L 1840, p. 287 ; Tr. Am. 



Phil. Soc, Vin, 1842, p. 201, pi. XI. fig. 14; Obs., IH, 1842, 



p. 39, pi. XI, fig. 14. — Chenu, 111. Conch., 1858, pi. xxxi, figs. 



4, 4a, 4b. — KusTER, Conch. Cab. L^nio, 1862, p. 287, pi. xcvi, 



fig- 5- 

 Margaron (Unio) fatmis Lea, Syn., 1852, p. 38; 1870, p. 61. 

 Lampsilis fatuus Simpson, Syn.. 1900, p. 553. 

 Unio dactylus Lea, Pr. Am. Phil. Soc., L 1840, p.. 287 ; Tr. Am. 



Phil. Soc, Yin, 1842, p. 196, pi. IX, fig. 7; Obs., Ill, p. 34, 



pi. IX, fig. 7. — Chenu, 111. Conch., 1858, pi. xxx, figs. 5, 5a, 



Margaron (Unio) dactylus Lea, Syn., 1852, p. 36; 1870, p.. 57. 

 I formerly doubted whether this species was distinct from 

 L. iris, but a recent examination of additional material con- 

 vinces me that, though there are intermediate specimens, it is a 

 valid species. It is generally longer in proportion than iris, 

 it has a higher posterior ridge, it is less rayed and the rays 

 are more entire, the posterior part of the shell is darker, the 

 teeth are smaller and the front half of the shell is very much 

 thicker. The thin hinder part of the nacre of fatua is beauti- 

 fully iridescent, with shades of blue and green predominating. 



Lampsilis peanicostata (Lea). 



Shell long elliptical or slightly rhomboid, subcompressed, 

 scarcely subsolid, with low, compressed beaks that have irreg- 

 ular, doubly-looped sculpture ; surface with faint irregular, 

 concentric growth lines, greenish-yellow, with broken, narrow 

 or wide, green ravs, which are often somewhat alternately ar- 



