190 ZOOLOGY. 
each side of which are attached a row of pinnules. Be-. 
sides Pentremites are the typical genera Hiwacrinus and 
Eleatherocrinus. 
Order 3. Cystidee.—This group is likewise extinct. In 
the fossil Pseudocrinus there is a short-jointed stalk, while 
in Caryocystites (Fig. 132) there is no stalk and no arms, the 
Fig. 182. - Caryocys- 
tites, a Gystidean 
After Liitken. 
Fig. 134.—Agelacrinus, a Cystidean, on 
the shell of a Brachiopod.—After Liitken. 
Fig. 138. —Pseudocri- 
nus, a Cystidean.— 
After Liitken, 
body being angulo-spherical, composed of solid plates. The 
Cystideans (Figs. 132 to 134) 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. They are the primitive Echinoderms. 
Crass I.—CRINOIDEA. 
Spherical or cup-shaped Echinoderms, without a madreporic plate, ust 
ally attached by a jointed stem, a few free in adult life, with five arms sub- 
dividing into pinnule ; 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 pinnule are usually present, though absent in Caryocystites. 
Circulatory, water-vascular, and sexual organs much as in other Echine 
derms ; the digestive canal ending in a distinct eccentric wperture, 
