28 



ASTEROIDEA. 



Sten ASTER. — Billings. 



Stenaster Salteri^ Billings. Geol. Surv. Canada, Organic Remains, pi. x, fig. 1 a, b, 

 p. 78. 



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 

 outwards. 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 specimens they taper uniformly from the body outwards. 

 The adambulacral plates are oblong, and the sutures between them are nearly at right 

 angles to the ambulacral grooves ; those next the body are a httle sloping outwards. 

 Their length is about twice their breadth, and they are so disposed that the greater 

 dimension is transverse, or at right angles to the groove ; the extremities which lie next 

 to the grooves are angular, and some of them appear to have the contiguous pores partly 

 excavated in them. The oral plates are acutely triangular, the sharpest angle being 

 towards the mouth. The plates are smooth. The ambulacral pores are very large, and 

 the ossicles are much contracted in the middle, and greatly expanded along the median 

 line of the bottom of the groove. 



The most perfect specimen is one inch in diameter, measured between the tips of 

 the rays ; diameter of disc, three lines ; width of ray at mid-length, two lines and a half. 

 Dedicated to J. W. Salter, Esq., Palseontologist of the Geological Survey of the United 

 Kingdom. 



Locality and Formation. — Belleville, Canada West ; Trenton Limestone. Collected 

 by Dr. Billings. 



Stenaster pulchellus. Billings. Geol, Surv. of Canada, Organic Remains, decade iii, 



pi. X, fig. 3, p. 79. 



Description. — Rays long, slender and sub-cylindrical ; adambulacral plates, transversely 

 oblong ; grooves narrow ; dorsal plates small and tubular. Diameter of the only specimen 

 in the collection two inches and one fourth, measured between the tips of the rays ; arms 

 one inch in length, and two lines and a half in vsddth at the base ; disc three lines and a 

 half in diameter. 



Locality and Formation. — Ottawa ; Trenton Limestone. Collected by Dr. Billings. 



