NO. 8 EDRIOASTEROIDEA — BASSLER 9 



curved and passing on to aboral surface ; floor plates arranged in two 

 series, one on each side of the ray, and alternating along the median 

 line. 



EDRIOASTER Billings, 1858 



(Cyclastcr Billings, 1857, not Cotteau, 1856; Agelacrinites Forbes, 1848, 



not Vanuxem ; Edriocystis Haeckel, 1896; Aesiocystites Miller and 



Gurley, 1894; Aesiocystis Bather, 1900) 



Sacklike, flexible theca attached by a small central portion of the 

 aboral surface and with the ambulacra passing from the oral to aboral 

 sides. Interambulacral plates mosaic. Ambulacra strongly curved, 

 four (1-4) to the left and one (5) to the right, with an anal pyramid 

 composed of many small plates, irregularly arranged. 



Genotype. — Cyclasfer bigsbyi Billings, 1857. Ordovician (Trenton) 

 of Canada. Agelacrinites buchianns Forbes, 1848, Edrioaster levis 

 Bather, 1914, E. saratogensis Ruedemann, 1912, and Aesiocystites 

 priscus Miller and Gurley, 1894, are other species of this genus. 



DINOCYSTIS Bather, 1898 



Oral surface convex, with five narrow ambulacra all strongly curved 

 to the left and aboral surface composed of a thin flexible integument 

 of narrow imbricating plates with a small central orifice for attachment. 



Genotype. — D. barroisi Bather, 1898. Devonian of Belgium. 



Family CYATHOCYSTIDAE Bather 



Edrioasteroidea in which the aboral portion consists of a fused solid 

 mass of plates attached permanently to some foreign object. 



CYATHOCYSTIS Schmidt, 1880 



Theca with oral surface much as in Stroniatocystites but mounted 

 upon a solid fused mass of stereom and permanently attached at the 

 aboral end. 



Genotype. — C. plautini Schmidt, 1880. Ordovician (Echinosphe- 

 rites limestone) of Estonia. 



CYATHOTHECA Jaekel, 1927 



Like Cyathocystis, except that the ambulacral areas are apparently 

 very narrow, practically hidden at the surface. 



Genotype. — C. suecica Jaekel, 1927. Ordovician of Sweden. 



