108 



ZOOLOGY. 



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

 sides Pentremites are the typical genera Elceacrinus and 

 Eleatherocrinus. 



Order 3. Cyst.idew. 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. 09. Caryocys- 

 tites, a Cystideau. 

 After Liitkeu. 



Pig. 71. Agelacrinvs, a Oystidean, on 

 the shell of aBrachiopod. After Liitkeu 



Fig. 70. Pseudocri- 

 nus, 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, usu- 

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

 dividing into pinnules ; the ambulacral feet in the form of tentacles 

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

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

 sent, but the pinnulce are usually present, though absent in Caryocystites. 

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

 derms ; the digestive canal ending in a distinct eccentric aperture. 



