South American Naiades : a contribution to the knowledge of the freshwater mussels of South America . 1); anal oi)ennig oiien or closed above, but . h ,^ * n d r-i i ?^ 1 & 1 ! Inner gill; n, Outer gill; p, Pes; s, ( losetl there never is a supra-anal openhig. (In the p,„.t of anal opening; t, Union of mantle Unionidce, the anal maj be open, but, when separating anal and hranehial openings. closed, there is alwajs a supra-anal opening.) ^ In Africa there are also Uiiioniilw of the subfamily Viiiimiiiiv: they undouhteilly point to a con-nection with Asia, since such forms are plentiful there, a
South American Naiades : a contribution to the knowledge of the freshwater mussels of South America . 1); anal oi)ennig oiien or closed above, but . h ,^ * n d r-i i ?^ 1 & 1 ! Inner gill; n, Outer gill; p, Pes; s, ( losetl there never is a supra-anal openhig. (In the p,„.t of anal opening; t, Union of mantle Unionidce, the anal maj be open, but, when separating anal and hranehial openings. closed, there is alwajs a supra-anal opening.) ^ In Africa there are also Uiiioniilw of the subfamily Viiiimiiiiv: they undouhteilly point to a con-nection with Asia, since such forms are plentiful there, and this indicates a dilTerent route of immigra-tion from that of the Mulelliur. The name depends upon the investigation of the anatomy of the African genus Mtilela, which isunknown, but we have every reason to assume, chiefly through Von Iherings study of the shell, thatthis genus will fall un<ler this family. The family name Mulditlw was lirst used by II. & A. Adams(1858), but for an entirely different association of forms. The Muklidai of Simpson (1900) correspondto our 456 MEMOIRS OF THE CARNEGIE MUSEUM. 4. Gills with or without water-tubes, and with isolated, scattered inter-laminar connections, or with interrupted or solid septa. (In the Unionidce, mostlyuninterrupted septa and water-tubes are found; very rarely are they interrupted;the forms with the latter probably form the connection with the Midelidw.) 5. Marsupium only in the inner gill (Figs. 1, 2, 3, i). (In the Unionidce, themarsupium is either in all four gills, or in the outer gills, never in the inner gillsalone.) 6. Certain advanced genera of the Mutelidw show a tendency to close thebranchial opening in front by a mantle connection. (Such a connection is entirelyunknown in the Unionidce.) The foregoing are the anatomical characters. The shape of the shell and itsparts are subject to so many variations, both in the Mutelidce and the Unionidce,that it is practically impossible to point out general
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