368 Mr. H. Seeley on Cambridge Palceontology : — 



It has already been seen that there is a surface for attachment, 

 towards which the visceral cavity enlarges ; so that if the or- 

 ganism were attached, the viscera would only be separated from 

 the surface beneath by the investing membrane — a character 

 almost inconceivable in a bony Echinoderm, since the internal 

 organs are always well protected. Then, there is no evidence of 

 that important structure, the mouth, which in all Echinoderms 

 is prominently developed ; and finally, there is no appearance 

 of the radiate plan, which is always self-evident in the bony 

 structures of the class. These facts render it certain that 

 each fossil is not an independent creature, but only a portion 

 of something else. What this is, there will not be much diffi- 

 culty in discovering, since it is a universal rule that Echino- 

 derms are made up of similar parts. The number of these 

 varies, the typical number being five ; but it must not be for- 

 gotten that many of the Echinoidea (which our fossils externally 

 so much resemble) present a very evident bilaterality. Now, if 

 two of them are united by the attachment surface, a free crea- 

 ture is produced, in which there would be a large central cavity 

 on one surface, where the mouth might well be placed ; while 

 the union produces, on the opposite surface, a much smaller 

 opening, which might be the anus; moreover, there is thus 

 obtained a symmetry which it would be impossible to suppose 

 wanting in a creature of this kind. But it is obvious that while 

 an animal would thus be produced presenting evident affinities 

 to both the Asteroidea and Echinoidea, it would difi*er from the 

 radiate plan in a way that those affinities would not induce us 

 to think probable. All the parts and organs would be in twos 

 instead of fives. According to this view of their structure, the 

 groove already referred to would hold the ambulacra ; and as 

 these are confined to the ventral surface;, the affinity to the As- 

 teroidea would clearly be greater than that with the Echinoidea, 

 so that there will be no reason for supposing them to be bi- 

 lateral on account of any resemblance to the latter order; while 

 the obvious resemblance of each specimen to the solidified ray 

 of a bony star-fisli is so great as scarcely to allow of a doubt 

 that these lobes or rays were arranged in fives, as in the mem- 

 bers of that group and the majority of Echinoderniata*. But it 

 will be asked — where is the disk ? Before answering that ques- 



* As the parts have but one articiihiting surface, and were grouped in 

 fives, they clearly must have been placed round a centre, as in Star-fishes 

 and Crinoids. The facts of there being no attachment for arms, there being 

 tubercles, and the stem not having been discovered, will be conclusive 

 evidence that their plan of structure was not that of the latter order. So, 

 as analogy would liavc suggested, we must adopt the only alternative, and 

 believe them to have been grouped round a disk as in Star-fishes. 



