144 



ECHINODERMATA. 



ORDER BRACHIATA. 



The true Criiioids have a calyx, with large piinmlated arms, 

 grooved on the upper surface, and bearing the reproductive 

 organs. The class description applies particularly to this order ; 

 also as relating to geological distribution. Eight genei-a are now 

 known to be living. Rhizocriniis is a widely distributed deep 

 sea form, being found as deep as 1,000 fathoms. Comaster, Ac- 

 tinometra and Antedon {Comatida), are free when adult. 



No. 437. [864, Cast]. Actinocrinus proboscidians, Hall. 



The Actinocrinoids, found chiefly in the Carboniferous 

 limestone, are sometimes provided with thorn like side arms, 

 which project from the column at irregular distances. The 

 receptacle is of an irregular subspherical form, and frequently 

 having arms passing off at right angles like the spokes from 

 the nave of a wheel. This species is from the Burlington 

 limestone (Carboniferous), Burlington, Iowa. 



No. 438. Actinocrinus verneulianus, Simm. 



Burlington Limestone (Sub-Carboniferous), Burlington, Iowa. 



No. 439. [898, Cast]. Apiocrinus Parkinsoni, Schloth. 



Two bodies and two stems branching from one root; 

 young. The "Pear-encrinites" have a complicated, ex- 

 panded root, a long column composed of numerous 

 ossicles, and a pj'riform receptacle, with arms well de- 

 veloped and regularlj^ bifid. The stem is round and not 

 pentagonal, and the articulating surfaces of the joints 

 are marked by simple ridges. The last joints increase 

 in diameter until they equal the breadth of the calyx. In 

 this species the stem is comparatively short. This speci- 

 men, consisting of two individuals of nearly equal de- 

 velopment, is fro;n the Great Oolite, Bradford, England. 



Size, 6x3. 



No. 440. [904, Cast]. Astrocoma Cirini. 



This beautiful Comatula or " Feather- star," with its numerous arms grace- 

 fully spread out, is from the Lithographic Limestone (Middle Oolite), Cirin, 

 France. Size, 7x4. 



