108 



ZOOLOGY. 



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

 sides Pentremites are the typical genera Mceacrinus 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.— Oan/ocys- 

 iites, a CyBtidean. — 

 After Liitken. 



Fig. 71.—Agelacrinus, a Cystidean, ou 

 the Bnell of aBrachiopod.— After Lutkeu 



Pig. 70.— Pseudocri- 

 nus^ a Cystidean. — 

 After Liitken. 



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 Echvrwderms, wiCnout a madreporic plate, vxu- 

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

 diwding into pinnuke; the atniulacrai feet in the form of tentacles 

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

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

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

 Circulatory, water-vascular, and sexual organs much as in othei' Echini 

 dermis ; tlie digestive canal ending in a disUnet eccentric aperture. 



