on respiratory function of Aristotle's lantern, [527];

on pedicellariae of Sphaerechinus, [541]

Uintacrinus, [588]

Ulmaridae, [324]

Ulmaris, [314], [324];

U. prototypus, [315], [324]

Umbellula, [331], [359], [360], [363];

U. gracilis, [359]

Umbellulidae, [362]

Umbrella of Medusae, [251]