Crinoids are marine invertebrates of unsurpassed variety of form and complexity of skeletal organization. They range from Early Ordovician time to the present, but their development in kinds and numbers culminated during the Paleozoic.

The evolution of fossil crinoids is an especially interesting study, because modification in different directions may be observed in each of several structural features. Also, evolution along one line may be accelerated greatly as compared with others. Investigation of the crinoids has special value in elucidating principles of evolution, and conclusions as to the nature of evolution among these organisms provide a basis for a classification...