ECHINODERMATA — CYSTOIDS 



155 



They are extinct, being confined entirely to the Paleozoic. 

 They extend from the Cambrian to the Permian, inclusive, with 

 maximum development in the Ordo\dcian and Silurian. 



Derivation of name. — Greek, cystis, bladder, + eidos (oid), 

 form, in allusion to the globular shape of most of the species. 



la- 



M 



B 



M. 



Fig. 59. — Caryocrinus ornatus Saj', from the Niagara shales (Middle Silurian) of 

 western New York. A, calj^x of a large specimen (natural size) with stem and 

 arms missing. B, inside of one of the plates (slightly enlarged),. showing the water 

 tubes, with an opening at their inner ends, an., anus, protected by a valvular 

 pyramid; st., position of stem; tu., tubes. (After Hall.) 



Caryocrinus (Fig. 59). Ordovician to Silurian. 



The principal portion of the body, a sub-globular hollow ball, 

 called the calyx, contained the digestive and blood vascular 

 systems. This calyx was anchored to the ground by a long, 

 jointed stem. The food grooves (ambulacra) radiating from 

 the mouth terminate in six to thirteen feeble arms. Both mouth 

 and food grooves are within the upper part of the calyx. Upon 

 the outer surface of each calyx plate, except the summit one, 

 are five or six single or double rows of pores radiating from its 

 center. Each of these pores is prolonged upon the inner sur- 

 face of the plate into a straight calcareous tube (Fig. 59, tu) which 

 in turn opens by a pore upon a bordering plate. All the tubes 



