108 



ZOOLOGY. 



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

 sides Pentremites are the typical genera Elceacrinus and 

 Eleatherocrinus. 



Order 3. Cystidece. This group is likewise extinct. In 

 the fossil Pseudocrinus there is a short- join ted stalk, while 

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



Fig. 69. Caryocys- 

 tites, a Cystidean. 

 After Lutkeu. 



Fig. 71. Agelacrinus, a Cystidean, on 

 the shell of a Brachiopod. After Liitkeu 



Fig. 70. Pseudocri- 

 nus, a Cystidean. 

 After Lutkeu. 



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, a few free in adult life, with five arms sub- 

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

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

 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. 



