﻿22 TRLiNCII.r.A 



ang'ular to siilirhomboid, usually hianq;ulate at the termination 

 of the posterior ridjje, the radial depression deeper than in the 

 female shell. Female shell not inflated, subrhomboid or sub- 

 quadrate, with a wide, rounded marsupial swelling just be- 

 hind the middle of the base. 



Length (male) 59, height 47, diam. 35 mm. 



Length (male) 48, height 40, diam. 24 mm. 



Length (female) 41, height 30, diam. 19 mm. 



Tennessee River. 



Type locality, Chattanooga River, Tenn. 

 Unio stczvardsoni Lea, Tr. Am. Phil. Soc., X, 1852, p. 278, pi. 



XXIII, fig. 36 ; Obs., V, 1852, p. 34, pi. XXIII, fig. ^6. — Reeve, 



Conch. Icon., XVI, 1864, pi. xv/ fig. 66. 

 Margarun (Unio) steward so ni Lea, Syn. 1852, p. 20; 1870, 



TrunciUn stczvardsoni Simpson, Syn., 1900, p. 521. 



Evidently very closely related to T. foliata, but a smaller 

 species in which the peculiar characters are less exaggerated. 

 The radial depression in the male shell is not so deep or dis- 

 tinct as it is in foliata. In the female shell it is quite feeble 

 and runs into the marsupial swelling where it is generally ob- 

 literated, while in foliata it continues down to the base of the 

 shell, behind the marsupial swelling. 



Subgenus Pilea Simpson, 1900. 



Pilea Simpson, Syn., 1900, p. 522. 



Male shell with a wide, shallow, radiating depression in 

 front of the posterior ridge, that of the female with a rounded, 

 foliaceous swelling at the posterior base. z\nimal with the post- 

 basal flap of mantle of female very heavy ; ovisacs not extend- 

 ing to the top of marsupium. 



'I\pe : l.^nio personatiis Say. 



Group of Trnncilla f^rrsonata. 



Shell inflated, rather solid, nearly as high as long ; female 

 not having a central depression, post-basal swelling small. 



