Turning to fossil Asteroidea, we find the earlier ophiurids scarcely distinguishable from the asterids, while in the alternation of the ambulacrals, which undoubtedly correspond to the flooring-plates of Edrioaster, both groups approach the Pelmatozoan type.

There is no difficulty in deducing the highly differentiated asterids and ophiurids of a later day from these simpler types.

3, D) and ophiurids (fig.

Turning to fossil Asteroidea, we find the earlier ophiurids scarcely distinguishable from the asterids, while in the alternation of the ambulacrals, which undoubtedly correspond to the flooring-plates of Edrioaster, both groups approach the Pelmatozoan type.

There is no difficulty in deducing the highly differentiated asterids and ophiurids of a later day from these simpler types.