Organic Remains. 225 



cup. In Ghjptocrinus the first or lowest primary radials rest 

 upon the upper edges of the basal plates, alternating so that each 

 ray is supported by the contiguous sides of two of the basals. In 

 Rhodocrinus there is a series of sub-radials between the basals and 

 primary radials. In such genera as Palceocrinus, Carabocrinus, 

 Dendrocrinus, and Porocrhms, the first primary radial only is in- 

 cluded in the walls of the cup, but the second plate and all above 

 it are free. In the very remarkable genus Cleiocrinus the pri- 

 mary, secondary, tertiary, quaternary and quinary rays are all firmly 

 connected together, the free arms commencing with the sixth or 

 seventh division." 



"The student will find many other modifications of the radial 

 system of the Crinoideae by consulting various palaeontologists ; 

 but the above are the more common ones, and those most preva- 

 lent in the Lower Silurian of Canada." 



VI. The Inter-radials. 



" The divisional space between two rays is called an inter-radius ; 

 and as there are five rays, there must be of course an equnl num- 

 ber of inter-radii. Four of these are always of equal size, and are 

 called the u regular inter-radii," and when they contain plates 

 these are designated the " regular inter-radials." The fifth is 

 larger than either of the other four, and is called the " azygos 

 inter-radius," from the Greek azugos, " unyoked," or " not paired.' 

 The plates in this inter-radius are called the azygos inter-radials. 

 In most works the " azygos inter-radials" are termed " anal plates," 

 but as they are not anal plates, I think another name preferable. 

 The azugos inter-radials always mark the anterior side of the ani- 

 mal or that side towards which the mouth is most approximated. 

 The posterior is directly opposite, and indicated by the azygos 

 ray. There are thus in every Crinoid two pairs of rays, the right 

 and the left, and an odd or azygos ray. There are also two pairs 

 of inter-radii, the right and left pair?, and an odd one, which is 

 the azygos or anterior inter-radius. When a Crinoid is placed 

 with its anterior side towards the observer, the left anterior ray is 

 opposite his right hand and the right anterior ray opposite his left. 

 Such genera as GlyptocrirMS and Rhodocrinus have both regular 

 and azygos inter-radials, but Paheocrinus, Carabocrinus and other? 

 of a similar structure, have only the latter." 



Cahad. Nat. 5 Vol. IV. No. 3. 



