Aquatic organisms, minute, distribution of, [47] n.

Arachnactis, [373], [411];

A. albida, [411];

A. americana, [411];

A. lloydii, [411]

Arachnoides, [549]

Arbacia, [520], [538]

Arbaciidae, [530], [531], [532], [538], [558]

Arbacioid type of ambulacral plate, [531], [538]

Arcadomyaria, [324]