105 



Fig, 66, 

 7711'^ ^aS 



as 



Fig. 67, 



mvs 



as 



Fig. 68, 



Fig. 69, 



Fig. 70, 



Fig. G4. The upper part of Caryocrinus ornatus,the test being removed in order to show the 

 internal structure of the fourteen hydrospires that surround the summit. The parallel 

 lines represent the flat tubiS. The other figures exhibit the modifications which the 

 hydrospires undergo in passing through : 65. Codaster. 66. Pentremites with broad 

 ambulacra. 67, Pentremites with single tubes. 68. Palseozoic Crinoida with a convolu- 

 ted plate attached to the centre of radiation. 69. Sand canal or madreporic tube of a 

 starfish inclosing a doubly convoluted plate. 70. Ambulacral canals of a starfish with 

 the doubly convoluted plate of the sand canal attached to the oesophageal ring. The 

 following letters have the same reference in all the figures in which they occur: a, an 

 arm or ambulacrum ; m v, mouth aud vent combined in a single aperture ; mvs, mouth, 

 vent and spiracle ; ambulacral groore; ovarian pore ; s, spiracle; c p, convolu- 

 ted plate ; r, oesophageal ring. 



arrangement. Thej were also, according to our present knowledge, the 

 first to make their appearance, two of the genera, TrochocjStites and Eocys- 

 titcs, having been discovered in the primordial zone. No other echin- 

 oderms have been found in rocks of so ancient a date. 



Next in order may be placed those genera whose test is composed of a 

 definite number of plates, which have^ to some extent, a quinary arrange- 

 ment. Thus, Ghjptocystitcs^Echinoencrinites, Apiocystitcs and several 

 others, have each four series ofcalycine plates, of which there arc four 

 plates ill the basil and five in each of the other three series. The respira- 

 tory areas or hydrospires are reduced in number — ten to thirteen in Ghji)- 



