the Crinoidese and the Echinodermata. 289 



Again, if we take an Echinus and separate the plates down the 

 middle of the interambulacral spaces and fold them back so as 

 to meet above, and then turn down the separated bands, we have 

 a complete Star-fish with the ambulacra and mouth beneath as 

 in the Asteriadce generally. Likewise, if an Echinus is placed 

 with the mouth upwards, we find the central plate beneath the 

 proper axis. This not inaptly represents the upper joint of the 

 column to which it bears considerable analogy. The five oviducal 

 plates may be considered as corresponding to the quinquepartite 

 dorso-central plate of the Apiocrinus, in which are seen the open- 

 ings of the oviducts. Above these pieces are the double range 

 of hexagonal plates which indifferently represent the perisomic 

 plates, rays, &c, of the Crinoid. 



Having traced the gradual transition from the Asteriadce to 

 the Crinoidece, from the Crinoidece to the Blastoidea, and from 

 these again to the Echinidce, and these last into the Star-fishes, 

 it now only remains to notice the Cystidece or Sphceronida, in 

 which analogies and gradations may be traced connecting them 

 with the Pentremites and Crinoidece, as well as with the Asteriadce 

 and Echinidce, in a similar manner to those links which I have 

 endeavoured to indicate in the preceding observations as existing 

 between the different groups of Echinoderms, but which will 

 however form the subject of further investigation. 



The Cystidece is an order of radiated animals which has long 

 been known to naturalists, but until recently no attempt was 

 made to place them in a position which their geological and 

 zoological importance seemed to demand. Mr. Gray of the 

 British Museum was the first, I believe, to see the necessity of 

 establishing a family for the grouping together of those ancient 

 forms of Radiata which closely resemble true Crinoids, but which 

 are devoid of arms, properly so called. With this view Mr. Gray 

 appears to have proposed the name of Sphceronidce for the group. 

 Subsequently Baron von Buch, in his essay. " Ueber Cystideen," 

 published at Berlin in 1845, grouped them together under the 

 above title. But I reserve further observations on this portion 

 of the subject to another opportunity, remarking however that 

 Prof. E. Forbes, at p. 531, part 2. vol. ii. of the ' Geological Me- 

 moirs/ seems to doubt the occurrence of Cystideans in our Moun- 

 tain Limestone, and asserts that the bodies I have described as 

 such he has " inspected through the kindness of Mr. Morris, and 

 they appear rather to belong to a group along with Pentremites 

 rather than to true Cystidea" 



In reply to this observation I can only remark, that the speci- 

 mens in my possession were not seen either by Prof. Forbes or 

 Mr. Morris, and that I ventured to group them with the Cystidea 

 on the authority of Von Buch himself, who founded the family, as 



Ann. | Mag. N. Hist. Ser. 2. Vol viii. 19 



