On a new Order of Echinoderms. 369 



tioii, it will be well to find out what kind of disk it had. That 

 it was not in one solid piece may be assumed, since it has never 

 been discovered ; and had it existed, it would have given a 

 rigidity to the body which we should not be justified in pi*c- 

 supposing without the most decided evidence to that effect. In 

 many specimens, the dorsal margin of the articulating surface 

 has an impressed border, as in some fossil Goniasters. On the 

 attachment-end may be detected three articulating surfaces — 

 one very narrow dorsal one, which is horizontal and curved in 

 rather less than a fifth of a circle, and two lateral ones, which 

 are vertical and do not generally extend quite to the base of the 

 side. The dorsal articulation will suggest the probability of the 

 dorsal surface being covered with minute triangular plates, re- 

 sembling those of the Brittle-stars, as Ophiothrix. This will 

 be further considered presently. The two lateral articulations 

 were probably, as in all Star-fishes and Brittle-stars, connected 

 with little bones which made the rays continuous with the bony 

 ring which probably surrounded the mouth. Thus there will 

 be no difficulty about the disk, since the minute size, rarity, and 

 the almost impossible task of determining what they were will 

 readily account for the circumstance of its elements not having 

 been detected. 



It would seem that a final conclusion may now be drawn. It 

 was before seen that the fossils belonged to a new group of 

 Echinoderms, and it has been shown that each was not a sepa- 

 rate animal ; that there is no reason for believing that the crea- 

 ture to which they did belong diverged from the radiate plan ; 

 and finally, and as the only explanation which was supported by 

 anatomical structure, it has been shown that they must have 

 formed part of an animal very closely resembling a star-fish. 

 Hence it will be admitted that a place has been found for them 

 which is the only one logically possible. 



Structure and Affinities. — It will now be desirable to notice 

 the relations of these fossil bodies with other Echinoderms ; 

 but before doing so, it will be necessary briefly to describe 

 the parts which will have to be compared. It has been ob- 

 served that each lobe or ray is a sphere, sometimes elongated 

 and flattened at one end. The groove on the ventral side re- 

 sembles that on the under side of the ray of a star-fish ; and as, 

 from the structural characters, it is clear that, in order to have 

 moved, the creature must have been furnished with suctorial 

 feet, it is evident that in these grooves only could the ambulacra 

 have been placed ; but they differ from those of the star-fish in 

 the important feature that whereas in the latter only the outside 

 of the ray is seen, in the former the whole cavity is exhibited, 



