CHAP. IX.] THE DEEP-SEA FJUNA. 441 



another bifurcation, and seven or eight joints farther 

 on another, and so on, but more irregularly the 

 farther from the centre, till each of the five primary 

 rays has divided into from twenty to thirty ultimate 

 branches, producing a rich crown of more than a 

 hundred arms. The upper surface of each arm -joint 

 is deeply grooved, the lower arched; and from one 

 side of each, alternately on either side of the arm, 

 there springs a series of flattened ossicles. These 

 form the ultimate branchlets, or ' pinnules,' which 

 fringe the arms as the barbs fringe the shaft of a 

 feather. Unfortunately, most of the examples of 

 Pentacrinus asteria hitherto procured have had the 

 soft parts destroyed and the disk more or less injured. 

 One specimen, however, in my possession is quite 

 perfect. The body is covered above by a membrane 

 closely tesselated with irregularly-formed flat plates; 

 this membrane, after covering the disk, dips into 

 the spaces between the series of radial joints, and 

 with the joints of the cup completes the body-wall. 

 The mouth is a rounded opening of considerable size 

 in the centre of the disk, and opens into a stomach 

 passing into a short curved intestine which ends in 

 a long excretory tube, — the so-called ' proboscis ' of 

 the fossil crinoids, — which rises from the surface of 

 the disk near the mouth. From the mouth five 

 deep grooves, bordered on either side by small square 

 plates, run out to the edge of the disk, and are con- 

 tinuous with the grooves on the upper surface of the 

 arms and pinnules, while in the angles between them 

 five thickened masses of the mailing of the disk 

 surround the mouth like valves. These were at 

 first supposed to answer the purpose of teeth. The 



