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The odontopleurid trilobite Leonaspis deflexa (Lake) was functionally capable of life in two alternative attitudes. In the ‘resting’ attitude the whole body could lie outstretched on the sea floor, supported on the hindmost anterior denticles of the cephalon and on the genal, thoracic, and pygidial spines. In this attitude the body declined posteriorly.

In the ‘active’ attitude, however, the cephalon was tilted forwards through 25°, bringing the body up horizontally. The hypostome and presumably the mouth also could then have been brought into close proximity with the sea floor.

Leonaspis, Primaspis, Diacanthaspis, and Anacaenaspis are all functionally comparable. Dudleyaspis, Acidaspis, and other genera were specialised permanently for life in an attitude analogous to the ‘active’ posture of Leonaspis.

The life attitudes postulated for odontopleurids are compared with those of other trilobites and some comments are given on the evolution of the different patterns.