Let the reader picture to himself a star-fish borne upon the summit of a flexible stem firmly rooted in the soil, and he has a general idea of the zoophytes which compose the order of the Crinoïdea. Naturalists of the seventeenth century bestowed the name of _stone lilies_ on these curious products. This rather poetical name proves that the conformation of these creatures had at an early period attracted observation, presenting the naturalist with the most curious of his lessons. The encrinites raise, as from the dead, a whole world buried in the abyss of the past. At the present time only two genera of these zoophytes exist, whilst in the early ages of the world the ocean must have swarmed with them. Encrinites abounded in the seas during the transition and secondary epoch. It was one of the most numerous of the animal tribes which inhabited the salt waters of the ancient world. In traversing some parts of France, we tread under our feet myriads of these beings, whose calcareous remains form vast beds of rock. The encrinites gradually disappeared from the ancient seas; their species were diminished as the globe became older or modified in its conditions, so that at the present time only a few types remain in our seas--such as the _Comatula_ of the Mediterranean; _Pentacrinus_, the Medusa's-head of the Antilles; and the European _Pentacrinus_--all of them very rare, and probably destined soon to disappear, carrying with them the last reminiscence of the zoological races of the ancient world: and here lies the real interest which the Crinoïdea presents to the thinking man. The encrinites most common in the fossil state are _Pentacrinus fasciculosus_, belonging to the lias; _Apiocrinus rotundus_, which is found in the oolite or jurassic rocks; and _Encrinus liliformis_, which appertains to the Triassic period. These three fixed zoophytes seem to have existed in great numbers during an early age of the world--namely, the Silurian period. They attained their maximum of development during the Devonian age, after which they begin to decrease. According to M. D'Orbigny, there are thirty-nine genera found in the palæozoic rocks, two in the triassic, seven in the jurassic, five in the cretaceous, and only one in the tertiary strata. Of all these genera only one, namely, _Pentacrinus_, is found in the modern epoch to represent the varied forms of these the first inhabitants of the seas. The free Crinoïdæ, that is, those not rooted to the soil by a stem, of which the _Comatula_ may be considered the type, only appeared at a later period. They are absent in the palæozoic and triassic rocks, but appear to have attained their maximum of development in the jurassic period.