Encyclopaedia Britannica, 11th Edition, Volume 8, Slice 10

must be admitted, a theoretical conception due to a desire for symmetry, and was not confirmed by anything better than some erroneous observations on certain fossils, which were supposed to show a plate at the oral pole between the five orals; but this plate, so far as it exists at all, is now known to be nothing but an oral shifted in position. The theory was that all the plates just described, and more particularly those of the cup, which were termed "the calycinal system," could be traced, not merely in all crinoids, but in all Echinoderms, whether fixed forms such as cystids and blastoids, or free forms such as ophiuroids and echinoids, even--with the eye of faith--in holothurians. It was admitted that these elements might atrophy, or be displaced, or be otherwise obscured; but their complete and symmetrical disposition was regarded as typical and original. Thus the genera exhibiting it were regarded as primitive, and those orders and classes in which it was least obscured were supposed to approach most n