108 



ZOOLOOT. 



each side of which are attached a row of pinnules. Be- 

 sides Pentremites are the typical genera Elmacrinus and 

 Eleatherocrinus. 



Order 3. CystidecB. — This group is likewise extinct. In. 

 the fossil Pseudocrinus there is a short-jointed stalk, while- 

 in Caryocystites (Fig. 69) there is no stalk and no arms, the 



Fig. 69.— Caryocys- 

 ites, a Cystidean. — 

 After LtLtken. 



Fig. 71. — AQelacrinus, a Cystidean, oa. 

 the shell of aBrachiopod, — After Latkeu- 



Fig. 70. — PgeudocrU 

 KW5, a Cystidean.^ 

 After Liitkeu. 



body being angulo-spherical, composed of solid plates. The- 

 Cystideans (Figs. 69 to 71) originated in the Cambrian for- 

 mation, attained their maximum development in a number 

 of species in the Silurian, and became mostly extinct in the- 

 Carboniferous period. 



Class I.— CRINOIDEA. 



Spherical or cup-shaped Echinoderms, without a madreporic plate, wtru- 

 ally attached by a jointed stem, a few free in adult life, with fine arms sub- 

 dividing into pinnulm ; the atnbulacral feet in the form of tentacles-, 

 aj-ising around the mouth in the furrous of the calyx or situated on Hie- 

 jointed arms. In the Blastoidea and certain Cystideans tlie arms are ab- 

 sent, but the pinnula are usually pi'esent, though absent in Caryocystites^ 

 Circtilatory, water-vascular, and sexunl organs much as in other Echiru^ 

 derms ; tlie digestive canal ending in a distinct eccentnc aperture. 



