34 ASTEROIDEA. 



TiENiASTER. — Billings. 



This genus, according to Dr. Billings, differs from Protaster in the following particulars. 

 Frofasfer has a well-developed disc, also pores outside of the ambulacral ossicles, and 

 the oral plates are formed of two of the ambulacral ossicles ; whilst Taniaster has no disc 

 nor marginal plates, and the oral plates are formed of two of the adambulacral plates. 



These important distinctions justify the separation of the species into a separate genus, 

 which presents many affinities with the Ophinrida. 



Taniaster spinosus, Billings. 'Canadian Organic Remains/ dec. iii, pi. x, fig. 3, p. 81. 



Bescrijylion. — The specimens collected are about seven lines in diameter; the rays 

 linear-lanceolate, one line in width at the base, and covered at the sides with nnmerous 

 small spines. 



In the view of the enlarged specimen (pi. x. 3G), the ambulacral ossicles appear in 

 some places to alternate with each other, but this is owing to a distortion. Those on one 

 side of the furrow are opposite those upon the other. The adambulacral plates are 

 elongated, and so placed that the outer extremity of the one lies upon the inner extremity 

 of the next. The rays are flexible. 



Locality and Formation. — Falls of Montmorency, Trenton Limestone, collected by Dr. 

 Billings. 



Taniaster cylindricus, BilUugs. 'Canadian Organic Remains/ dec. iii. pi. x. fig. 



4., p. 81. 



Description. — About an inch and a half in diameter, or a little more ; rays sub-cylin- 

 drical, regularly rounded on the upper side, flattened on the lower, covered above with 

 spines; about a line in width at the base, and tapering to an acute point. 



This species is larger and more robust than the former. Both appear to be somewhat 

 common, and the specimens are often found with their rays variously curved, showing that 

 they were extremely flexible. 



Locality and Formation. — City of Ottawa, Trenton Limestone. Collected by Dr. 

 Billings. 



