ACEPHALA. 15 
MarcariTana, Schum. Gills free from abdominal 
sac, — their posterior extremity not united to the 
mantle; anal opening or region of mantle not fringed, 
branchial fringed. 
M. arcuata, Phil. Alasm. arcuata, Barnes. Gould, 
gis on ra 
AuasmoponTa, Say, emend. Gills attached to ab- 
dominal sac, attached also to the mantle to their ex- 
tremity ; branchial siphon fringed, anal large, not 
fringed. Eggs 2 
A. marginaTa, Say. Gould, 116, f. 77. 
Srropuitus, Raf.emend. Gills attached; eggs re- 
ceived in the whole extent of the outer gill; anal 
opening not fringed. 
S. unputatus, Raf. Anodonta undulata, Say. Gould, 
120) t79- 
S. scunprinis, Ag., MS. Unio undulata, Say. Alasm- 
undulata, Barnes. Gould, 115, f. 76. Alasm. sculp- 
tilis, Say. 
Anoponta, Brug. Gills free; eggs throughout the 
gill; anal opening not fringed. 
A. BenepicTensts, Lea. — Lake Champlain. 
A.impiicata, Say. Gould, 118, f.'78.— Eastern Mas- 
sachusetts. 
A. FLUVIATILIS, Lea. Gould, 117, f.80. Mytilus fluvi- 
atilis, Dill. 
A. MARGINATA, Say. 
A. Hovsatonica, Linsley, Conn. Cat. Gould, Am. 
Journ. 1848. 
A. suBcyLinDRAcEA, Lea. — Connecticut, (fide Linsley.) 
