The species of aphrosalpingid sphinctozoans earlier known from the Ludlow of the Middle Ural Mts of Russia, plus the new species Aphrosalpinx nana, Nematosdpinx hormathodes, Cystothalamiella alaskensis, and C. irregularis, are described from the Ludlow part of the Heceta Formation of southeastern Alaska. This is the most diverse assemblage of Silurian sphinctozoans known. Only one other sphinctozoan species was previously recorded from the Silurian. Aphrosalpinx textilis and Nematosalpinx dichotomica occur also in other localities of the Silurian in southeastern, southwestern, west-central and south-central Alaska; the type specimens of these species from the Ural Mts are redescribed. The similarity of Silurian sphinctozoan assemblages from Russia and Alaska points out the strong
paleobiogeographic relationship of the Nixon Fork terrane from west-central Alaska to the Alexander terrane of southeastern Alaska, and to the Ural Mts. Disjunct occurrences of several sponge species may also suggest ready access of marine faunas of northwestern North America and the Ural Mts region during the Silurian. The first recorded occurrences of a Ludlow orchoclad(?) sponge from southeastern Alaska are generically unidentifiable fragments from the Heceta Formation.

Key words: Porifera, sphinctozoans, systematics, Alaska, Silurian.