108 



ZOOLOGY. 



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

 sides Pentremites are the typical genera Elmacrinus and 

 EleatJierocrinus. 



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. — Caryoa/s- 

 iites, a Cyetidean.— 

 Af tur Liitkeu. 



Fig. 71. — Aqelacrinus, a Cyetidean, on 

 the shell of aBrachiopod. — After Llitkeu 



Fig. 70. — P^eudocH- 

 nits, a Cyytidean, — 

 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. 



Spheriail or cup-shaped Echinoderms, wifnout a inadreporic plate, usii- 

 ally attaclied by a jointed stem, a few free in adult life, with five arms sub- 

 dividing into pinnulm ; the amiulacral feet in the form, of tentacles 

 arising around the mouth in the furrows of the calyx or situated on (lie 

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

 sent, hut the jnnnidm are usually present, though absent in Oaryocystites. 

 Circulatory, water-vascular, and sexual organs much as in other Echino- 

 derms ; tlie digestive caned ending in a distinct eccentric aperture. 



