. A manual of zoology. Zoology. 343 ECniNODERMA. Sub Class I. Eucrinoidea. The foregoing account applies entirely to the Eucrinoidea, which may be divided into two groups : Order I. TESSELLATA (Palfeocrinoidea). Theea with its side walls composed of immovably united thin plates ; the ambulacral grooves usu- ally completely covered by calcareous plates. Exclusively paleozoic. Order II. ARTICULATA (Neocrinoidea). Ambulacral grooves open, theca witli compact, in part movably articulated, ]jlates. This order left the other in the mesozoic age, and some families have persisted until now. Rhizoarinu
. A manual of zoology. Zoology. 343 ECniNODERMA. Sub Class I. Eucrinoidea. The foregoing account applies entirely to the Eucrinoidea, which may be divided into two groups : Order I. TESSELLATA (Palfeocrinoidea). Theea with its side walls composed of immovably united thin plates ; the ambulacral grooves usu- ally completely covered by calcareous plates. Exclusively paleozoic. Order II. ARTICULATA (Neocrinoidea). Ambulacral grooves open, theca witli compact, in part movably articulated, ]jlates. This order left the other in the mesozoic age, and some families have persisted until now. Rhizoarinus* (fig. 323) and Pejitacrinus (fig. 320j, deep seas ; the Coma- are fixed in the young, free in the adult. Antedon* (fig. 321). Sub Glass II. Edrioasteroidea {Agelacrinoidea). Theca of irregular plates ; arms unbranched and lying on the theea. Possibly the ancestors of the noncrinoid echinoderms. Paleozoic. Agela- crinus. Sub Class III. Cystidea. Exclusively paleozoic ; body spherical, composed of polygonal plates. Stalk and arm structures rudimentary, sometimes lacking. The Ampho- RiDA are by some regarded as ancestral of all echinoderms. Holocystites, Echinospliarites (fig. 336).. Fig. 336. Fig. 327. Fig. 320.—-Ec/uno.'.p/ja'r/Yc.'; aura-ntiuni. (From Zitti'l ) Fig. 327.—P'^virefnUesJhiiPfili.'i. (From Zittcl). Lateral, oral, and alioral views. Sub Class 71'. /t'lastnidca. Arms lacking ; the mouth surrounded by five petal-like ambulacral areas. The group appears at end of Silurian and dies out with the earbon- iferous. I'cittreniites (fig. 327).. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Hertwig, Richard, 1850-1937; Kingsley, J. S. (John Sterling), 1854-1929. New York, H. Holt and Company
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