The genera of stalked Crinoids now living are the remains of a family that at one time had many representatives in all parts of the world. Nearly all the marine deposits of bygone epochs, including even those of such remote periods as the Cambrian and Sub-Silurian, contain the fossilised skeletons of these Crinoids. In some strata they are represented by only a few genera, but in others they are found in such enormous numbers that the seabeds of those early times must have been literally carpeted with them. At the present day the few genera that survive have been driven from the shore waters, and are chiefly found at depths of more than 200 fathoms, a few only extending into 140 and even 70 fathoms. [Illustration: FIG. 11.—_Rhizocrinus lofotensis_, one of the deep-sea stalked Crinoids. (After Carpenter.)] There are six genera known, and of these, two, _Hyocrinus_ and _Bathycrinus_, are not found in less than 1,000 fathoms of water. There can be no doubt that these modern stalked Crinoids are closely related to many of those that flourished in bygone periods of the history of the earth. As Carpenter has pointed out, the family Pentacrinidæ are remarkable for their long geological history. The genus _Pentacrinus_ itself first appeared in the Trias and persisted through the Secondary and Tertiary times to the present day. The general character of the fossil Pentacrinidæ is essentially the same as that of their recent representatives, except that they often had much longer stems which reached to a length of as much as 50 or even 70 feet; while the number of arms was frequently limited to ten, which is not the case in any recent species but _Pentacrinus naresianus_. But the deep-sea Echinoids, or sea-urchins, also present some features of particular interest. Professor Agassiz in his report says, ‘One of the very first results clearly indicated by the deep-sea dredgings of Count Pourtales and the subsequent investigations of the “Porcupine” expedition was the antique character of the new genera discovered in deep water, and especially their resemblance to the cretaceous genera; and the study of the “Challenger” Echinoids has brought this out still more clearly.’ No fewer than twenty-four genera extend into the abysmal regions; of these no less than sixteen, nearly all belonging to a new group of Spatangoids, do not live at all in shallow water. The most interesting forms among these are the Pourtalesiæ, a group that has existed since the Chalk. These are heart-shaped urchins with a very peculiar test. ‘They all have large coronal plates, recalling the Echini, with a disconnected apical system characteristic of many cainozoic spatangoids; they have a sunken anal system, some of them a most remarkable anal beak and a very striking pouch in which the mouth is placed.’ They are found only in very deep water, and have no allies among the modern littoral fauna.