On the AsTERiAD^ of the Lower Silurian RocJts of Canada. By E. 

 Billings, Esq., F. G. S. 



The following species of Star-fishes were described in the Report 

 of the Greological Survey published in 1857, page 290 et seq., with 

 the following introduction : — 



" The species of Star-fishes in the collection appear to be referrable to the genera pro- 

 posed by Mr. Salter at the meeting of the British Association, in August last. I have 

 seen no other description of these genera than that given in Silliman's Journal of 

 November, 1856, which is as follows : 



" Pal^aster. — Without disc, avenues deep. 

 " Pal^astbrina. — Pentagonal, disc moderate. 

 " Pal^ocoma. — No disc, avenues very shallow. 

 " It is probable that our species, when opportunity can be had for a direct compa- 

 rison with British specimens, will be found congeneric." 



Since then Mr. Salter has published full details of the above and 

 some other genera,* and I have also examined some of the species 

 described by him and Prof. Forbes. 



* On some New Palaeozoic Star-fishes. By J. W. Salter, Esq., F. G. S. Annals and 

 Magazine of Natural History, November, 185*J. 



The above diagram is given to explain the sense in which the following terms are 

 used in this memoir : 



a. Amhulacral ossicles, — the small plates in the bottom of the ambulacral furrows, 



between which the pores for the passage of the suctorial feet pass. 



b. Adamhulacral plates, — the rows of plates which border the ambulacral grooves, 

 m. Marginal plates, — the row of plates round the margin of some of the species. 



0. Oral plates, — situated at the angle of the mouth. In many species these consist of 



the ten terminal adambulacral plates. 

 Disc-plates, — I propose to call all the plates of the body which cannot be comprised in 



any of the above four classes, disc-plates. 



