76 , CANADIAN FOSSILS. 



After much consideration, I have resolved to adopt the following 

 arrangement for the Canadian species. 



Genus Palasterina, McCoy.* 



{As defined by Mr. Salter, 1857.) 



Generic Characters. — " Pentagonal, depressed ; the arms a little 

 produced, with three or five principal rows of tubercles above, com- 

 bined with a plated disk which fills up the angles ; ambulacra rather 

 shallow, of sub-quadrate or slightly transverse ossicles, bordered by 

 a single row of squarish large plates, the lowest of which {ad-oral 

 adambulacral plates, Huxley t) are large and triangular, leaving 

 combs of spines." 



The following species having been already placed in the above 

 genus, I am unwilling to create a new one for them until more is 

 known as to what constitutes a generic character among the Star- 

 fishes. Our specimens do not shew any spines, but perhaps they 

 have not been preserved ; and even could it be shown that P. stellata 

 was without these appendages, it would still remain to be settled 

 whether this difference is or is not of generic importance. 



I. Palasteeina stellata, Billings. 

 Plate IX. Fig. la, 15. 



(P. stellata, Geological Survey of Canada, Report, 1856, p. 290.) 



Description. — Pentagonal ; disc about one half of the whole diame- 

 ter ; ambulacral grooves narrow and deep, bordered on each side by 

 a row of small nearly square adambulacral plates ; a second row con- 

 sisting of disc plates extends nearly to the end of each ray, the 

 remainder of the disc covered with smaller plates. All of these plates 

 are solid and closely fitted together ; the disc-plates in the angles in 

 contact with the oral plates are much larger than any of the others. 



In the only specimen in the collection the length of the rays mea- 

 sured along the ambulacral grooves is three lines ; number of adam- 

 bulacral plates on each side of the grooves sixteen ; the rays diminish 

 somewhat rapidly in size, and terminate in a rounded point ; dia- 

 meter of the disc four lines. The plates are all a little worn, so that 

 the character of their surfaces cannot be observed ; they were pro- 

 bably nearly smooth. 



* Suggested by Prof. McCoy, who did not however define the genus. British Palaeo- 

 zoic Fossils, p. 59, 1851. 



t Angle-ossicula (Forbes), oral plates of this memoir. 



