ACEPHALA. 13 
those of other authors, and somewhat confused. I 
have therefore not referred to his work. 
UNIONIDA. 
Unio, Retzius, emend. Gills free from the abdomi- 
nal sac, their posterior extremity attached to the man- 
tle; eggs, in the female, filling the whole extent of 
the outer gill; mantle fringed at both siphonal open- 
ings. (Agassiz, MS.) 
U. compianatus, Lea. Gould, 107, f. 68. Mya com- 
planata, Soland. 
Evurynea, Rafinesque, emend. Gills attached to 
the abdominal sac, leaving no communication be- 
tween the pedal, and the upper gill cavities; eggs 
received in the sacs of the posterior part of the outer 
gill; mantle fringed at the posterior half of its ven- 
tral edge, and at the branchial and anal siphons. 
E. prevonea, Ag, MS. Unio prelongus, Barnes. — 
Lake Champlain. It is doubtful whether this spe- 
cies, of the North, is a variety of U. rectus, Lam., or 
not. (Ag.) 
E. nasura, Ag. MS. Mya nasuta, Wood. Unio na- 
sutus, Say. Gould, 109, f. 71. (non Lam.) 
—_—— Lampsius, Raf. emend. Gills attached; eggs in 
the posterior part of the outer gill; mantle fringed at 
both siphonal openings, and having fleshy thicken- 
ings and processes at its posterior ventral edge. 
L. rapiata, Ag., MS. Mya radiata, Gmel. Unio ra- 
diata, Lam. Gould, 110, f. 73. 
