366 Mr. H. Seeley on Cambridge Palceontology ,•— 



the fossil in question, has a groove for holding the nervous cord, 

 and there is a close analogy between all the parts. I am not 

 acquainted with any form in which the margins are tuberculated ; 

 but it is by no means impossible to conceive that they should 

 be so ; on the contrary, if the plate were so placed as to*have its 

 under side exposed, it would be precisely what we should expect. 

 This resemblance is certainly very close ; but, among many other 

 little differences, it will soon be observed that that pit in the groove 

 is wanting in the fossil which exists in the small ocular plate, 

 for lodging the enlargement of the nerve ; and when inquiry is 

 made for the plates of the star-fish to which these supposed 

 oculars belong, the difficulty becomes insuperable. I have seen 

 about one hundred and fifty of these structures, the largest a 

 quarter of an inch long ; so that there ought to have been col- 

 lected with them several thousands of granulated plates of two 

 or three species of Goniodiscus, of which each plate should have 

 measured from one to two inches in diameter ; whereas not a 

 single granulated plate has been found, and the only plates met 

 with are a few pitted ones belonging to an Astrogonium. This 

 must demonstrate that it has nothing to do with the Star-fishes ; 

 and thus the Class Echinodermata is exhausted without our finding 

 a place for it. We shall search in vain for a group with which 

 it presents a nearer affinity. The tubercles for the attachment 

 of spines constitute a character not met with in any other class 

 of organisms ; and the wdiole sum of the characters clearly indi- 

 cates that there can be no doubt as to the class to which these 

 singular bodies belong. 



The structure may give some clue to their real nature. As 

 already remarked, one end is fitted for attachment. If, then, it 

 is no part of an Echinoderm, and yet is Echinodermatous, it 

 would appear to be something attached to an Echinoderm. Now, 

 certain anomalous bodies, known as Pedicellarise, do occur at- 

 tached to Echinoderms. In the Sea-urchin group they are pe- 

 dunculated cups, with three moveable prongs. On Star-fishes 

 they consist of two little valves, like Entomostraca. On Cri- 

 noids I believe both of these forms are met with. To neither 

 do these fossils, in any way, approach; but they can scarcely 

 be considered to diff'er more from the sessile form on Star-fishes 

 than that does from the form occurring on Urchins; so the 

 fact of their being distinct from any known type does not neces- 

 sarily exclude them from the group. There arises, however, the 

 question — if Pedicellarise, on what creatures did they occur ? 

 Certainly not on Star-fishes ; for Prof. Forbes noticed, on a spe- 

 cies from the Greensand, structures of this kind apparently iden- 

 tical with the living form ; and it would be impossible to conceive 

 how so large a species could be attached to Diadema, which is 



