CLASS I 



CYSTOIDEA 



159 



majority of Cystids, extending from the Cambrian to the Lower Carboniferous. 

 Two genera, Agelacrimis and Edrioaster, are fairly abundant in certain localities 

 of North America, but the others are rare. 



Family 1. Agelacrinidae Hall. 



Calyx composed mostly of thin plates, flexible, attached temporarily or per- 

 manently by the greater part of the aboral surface ; ambidacra confined to the oral 

 surface. Cambrian to Carboniferous. 



Agelacrinus Vanuxem (Fig. 250). Calyx in the form of a depressed or 

 convex disk, stemless, and attached by the entire under surface ; composed of 

 numerous, small, polygonal, usually imbricating 

 plates, which are perforated by fine, usually 

 conjugate pores. Mouth surrounded by four 

 oral plates ; radiating from this are five small, 

 more or less curved food-grooves, which are 

 embedded in the disk, and are protected by a 

 double row of covering plates. Ordovician ; 

 North America, Rhineland and Bohemia. Rare 

 in Silurian and Devonian. 



Stromatocystis Pompeckj. Cambrian; Bohemia. 



Cystaster Hall [Thecocystis Jaekel). Streptaster 

 Hall. Ordovician ; Ohio. 



Hemicystites Hall. Ordovician and Silurian ; 

 North America and Bohemia. 



Haplocystis Roemer. Devonian ; Rhineland. 



Lepidodiscus Meek and "Worthen. Devonian to Carboniferous ; North 

 America. Discocystis Gregory, Carboniferous ; North America. 



Pig. 200. 



Agelacrinus cincinnatiensis Roemer. 

 Ordovician ; Cincinnati, Ohio. Indi- 

 vidual of the natural size adherent to 

 test oi Baflnesquina alteniata (Conrad). 



Family 2. Oyathocystidae Bather. 



Calyx composed on the oral surface of five deltoids surrounded by marginals, but 

 beloiv of a fused solid mass of stereom, with irregular longitudinal sutures ; ambu- 

 lacra confined to oral surface ; permanently attached by the aboral surface, as by an 

 encrusting roof. Ordovician. 



Cyathocystis Schmidt. Ordovician ; Esthonia. 



Family 3. Edrioasteridae Bather. 



Calyx flexible, composed of thin plates; attached, if at all, by a small central 

 portion of the aboral surface ; ambulacra pass on to the aboral surface. Ordovician 

 to Devonian. 



Edrioaster Billings (Aesiocystis Miller and Gurley) (Fig. 251). Ordovician ; 

 Canada and Kentucky. 



Dinocystis Bather. Devonian ; Belgium. 



1 Cyclocystoides Billings and Salter. Ordovician ; North America and Great 

 Britain. Probably a Cystid, but not sufficiently known to be assigned to any 

 particular family. 



