160 



ECHINODERMATA— PELMATOZOA 



PHYLUM IV 



Family 4. Steganoblastidae Bather. 



Calyx rigid, composed of plates relatively larger and thicker than in other 

 families of this group, including elements comparable to the radials and basals of 

 Blastoidea. Ambulacra descend into the radials. A short stem present. Ordovician. 



Sfeganoblastus Whiteaves {originally desci'ibed as Astrocystites, name pre- 

 occupied). In all the prominent external characters resembling a Blastoid, 

 but careful study of the type specimens by Bather has shown the ambulacra 

 to have essentially the same structure as ,in Edrioaster, and that brachioles are 

 absent. Ordovician ; Canada. 



am 



P arpt vg Q^ 



Fifi. 251. 



Edrioaster higshyi Bill. Ordovician ; Ottawa, Canada. 1, Oral surface with covering plates (auih) on two 

 of the grooves, and side- or floonng-i)lates (ad) on the others, x 1/1. 2, Vertical section of same, 1/1. 3, Sec- 

 tion across an ambulacrum, enlarged. Ad, flooring-plates; (i-mi'i, covering-plates ; an, anus; i.a, interanibu- 

 lacrals ; M, madreporite ; m, membrane with imbricating plates, thrown into live lobes (?) ; /, frame of stouter 

 plates ; 'ps, subtegminal peristome ; j/, pores ; v(j, ventral groove (after Bather). 



The following generic names have been incorrectly applied to Cystids : 



Probably a Camerate Crinoid. 

 {Loholithus BaiT.). Inflated or bullions root of the Caiiiei 



Ascocystites Barrande 

 Caiimrocrinus Hall. 

 Crinoid, Scyphocrinus. 



Cardiocystis Barraude. Indeterminable. 



Qrinocystis Hall. Probably a Camerate Crinoid. 



Oyclocrinus Eiehwald {Pasceolus Billings). Not an Echinoderin. 



Dictyocrinas Conrad. A Receptaculite. 



Hyponomc Loven. The ejected disk of a Coniatulid. 



Lichenocrimis Hall. The terminal stem-plate or root of some Pelmatozoan 



Neocystites Barrande. Probably the root of a Pelmatozoan. 



Porocrinus Billings. An Inadunate Crinoid. 



ate 



Range and Distribution of the Cystoidea. 



The Cystideans, a wholly extinct class, are the oldest known members of 

 the Pelmatozoa. They are represented in the Cambrian by a number of poorly 

 preserved foi'ms, whose affinities are in many cases doubtful {Protocystites, 

 Macrocystella, Eocystites, Lichenoides, Trodiocystites). They attain their maximum 

 development in the Ordovician and Silurian, whereupon they suddenly diminish 

 in numbers, and probably disappear in the early Carboniferous. Of the 250 

 species that have been described, scarcely a dozen are found in strata above 

 the Silurian. 



