38 ZOOLOGY. 



around the oesophag:us, with branches to tlie rays, &:c. The mouth is armed 

 with hard bony teeth, enabling tlie animal to live upon crnstacea and shell 

 fish. Some live at the bottom of the sea on the surface of the rock, and 

 others burrow in the sand. 



The integument of some of the members of this class is sustained by a 

 calcareous skeleton, which incloses the viscera and supports movable spines 

 varying much in size and shape. The skeleton is composed of pieces which 

 are often joined together like polygonal stones in a pavement. These 

 plates, the spines, and the entire skeletoTis, are very abundant in various 

 geological formations, in which they are preserved in great perfection. 



The class contains the orders Crinoidea, Asteridea, Echinidea, Holothuri- 

 dea, to which some add another for the reception of Siponculus, Echiurus, 

 itc, constituting the apodous Echinodermata of Cuvier. 



OiiDER 1. CRixomEA. This order is almost extinct, but is found plentifully 

 in a fossil state in the older rocks. These remains consist of the solid 

 calcareous skeleton, of which the chief parts are the stem, the body, and 

 the arms. The body is oval or cup-shaped, protecting the internal soft 

 parts, and made up of mimerous plates, of which the variations in number 

 and form afford generic characters. The arms are five or more in number, 

 simple or branched, fringed with lateral articulated appendages, and placed 

 around the upper margin of the body, the mouth being situated between 

 them. When the arms are closed, some species resemble a lily, whence the 

 trivial name of Enerinus lilUformis. The vent is distinct and lateral. 



The central solid part of the stem has been compared to the bones in a 

 lizard's tail, being made up of a column of disks, which are either circular, 

 polygonal, or star-shaped. The stem is often provided with articulated 

 simple lateral branches, which, like the arms, are filled with calcareous 

 joints, many thousand of which are contained in the remains of a single 

 animal. The disks of the stem have a perforation through them, which 

 admits of their being strung like beads; and, according to Dr. Buckland, 

 they were used for rosaries in ancient times. In northern England they are 

 called St. Cuthbert's beads ; and before their nature was known, they were 

 named Entrochites in books. 



Pentacrinns astcria, Linn. (P. caputmedusw, Miller) {pi. IQ^fig. 58), is 

 a recent species from the West Indies, of which a specimen is in the British 

 ^Museum, the Paris Museum, that of the Geological Society of London, and 

 that of the London College of Surgeons. (This and other species of the 

 order are figured in the Penny Cyc. ix. 390, and in the new edition of the 

 Pegne Animal.) Enerinus radlatus {fig. 57). 



Pentaciiniis 6'«^/'o^fews, Thompson, a minute animal found on the coast of 

 Ireland, is now considered by this author to be the pedunculated young of 

 Comatula, a starfish somewhat like pi. Y<), fig. 62. This confirms one of 

 the views of Agassiz (Lectures, p. 13), that the earlier fossil animals often 

 resemble the embryonic or immature forms of the more recent periods. 



IIolopus ra7igii, Orbigny {2?l. 76, fig. 56) (Mag. de Zool. 1837,^?. 3) is a 

 recent genus from Martinique. 



Order 2. Asteridea. In this order the supporting stem is wanting, and 

 242 



