78 CANADIAN FOSSILS. 



pores. Dorsal side of disc and rays covered with small plates, which 

 appear to be tubercular and not closely fitted together. The generic 

 name is from the Greek stenos, narrow, in allusion to the contracted 

 body. 



As it has been suggested that the two species hereinafter described 

 should be referred to Palceaster^ I give the following figure of that 

 genus in order to show the difference. 



Fig. 1, Palceaster Niagarensis, Hall. 



Upon examining the above figure, it will be seen that there is a 

 great difference between Stenaster and Palceaster, for the following 

 reasons : 



1. If the large plates which border the groves in Palceaster be 

 adambulacral, then there are only five oral plates, whereas in Sten- 

 aster there are ten. 



2. But if they be not adambulacral but marginal plates, then 

 Palceaster ranst have both marginal and adambulacral, while Stenaster 

 has only the latter. 



III. Stenaster Salter:, Billings. 



Plate X. Fig. la, lb. 



Description. — This species has rather short broad rays, which are 

 narrower where they are attached to the very contracted body than 

 they are at about the centre of their length. In consequence of this 

 form, the sides of the rays are not parallel, but a little curved out- 

 wards. As however only two specimens have been collected, and 

 both appear to be a little flattened by vertical pressure, it may be that 

 this leaf-like shape of the rays is accidental, and that in perfect spe- 

 cimens they taper uniformly from the body outwards. The adambu- 

 lacral plates are oblong, and the sutures between them are nearly at 

 right angles to the ambulacral grooves ; those next the body are a 



