THE 



GEOLOGICAL MAGAZINE. 



No. LXXXIV.— JUNE, 1871. 



I. — Notes on the Ckinoidea. 



By John Eofe, F.G.S. 



(PLATE VI.) 



WHEN reading the very interesting article^ in the "Student" 

 for October last, " On the Deep Sea," by Dr. Carpenter, I 

 was struck by the description of an Echinidan, which had been 

 dredged up, and which is represented as looking "externally like 

 a sea-egg flattened by pressure ; it was about five inches in diameter, 

 and of a brilliant crimson hue. Its test being composed of plates, 

 separated by membrane, instead of being united by suture, was 

 quite flexible, so as to resemble an armour of chain mail rather 

 than the inflexible cuirass with which the ordinary Echinida are 

 invested." This statement as to the flexibility of the test so cor- 

 responds with what I have long suspected to be the case with some, 

 at least, of the Crinoids, that I have been induced carefully to re- 

 examine a large number of specimens, both of heads and columns 

 of fossil, and to make some experiments on recent Crinoids ; and 

 I propose now to state shortly the result, and to suggest some points 

 for the consideration of those who may take an interest in such 

 subjects, and who are better qualified than I am, by their knowledge 

 of the animal kingdom, to give an opinion on them. 



That the Crinoidea, both recent and fossil, have or had flexibility 

 in their columns, rays, and side-arms, cannot admit of doubt ; the 

 two latter, from their nature and use, must have been flexible, and 

 sometimes fossil columns are found so much curved that they might 

 at a casual glance be mistaken for Ammonites, and they frequently 

 have the appearance of being furnished with a membrane or cushion, 

 intervening between the plates, expanded on the outer side of the 

 circle so formed, and contracted on the inner. A membrane so 

 situated would, like the intervertebral substance (cartilage) in the 

 vertebrata, evidently admit of this flexure, and such has been sup- 

 posed to exist by Messrs. Austin and others. The so-called screw 



1 "The Student," vol. v., 1870, p, 361. 



VOL. VIII.— NO, LXXXIV. 16 



