18 CANADIAN FOSSILS. 



There are at the present time known to be eleven species of 

 Crinoids in this formation, and of these five vrill be characterized in 

 the following pages ; but of the other six we have as yet only the 

 columns and some of the detached plates. Although we cannot 

 determine the genera of these six species, yet it is quite certain that 

 they are different, not only from those hereinafter described, but 

 also from each other. None of the species are clearly identical 

 with any that occur in either the Black River or the Trenton 

 limestones, although one, Hijbocrbws pristinns, is closely allied to 

 H. tumidus, and may perhaps be a variety thereof. 



The Crinoids and Cystideans of the Cbazy appear to have been 

 confined to a comparatively small area of the Silurian ocean. The 

 grey limestone in which they occur is exposed in numerous localities 

 on the islands of Montreal, Jesus, and Bizard, and in that tract of 

 Silurian country which lies between the Ottawa and St. Lawrence 

 rivers. It also extends from the island of Montreal southerly to the 

 neighbourhood of Lake Champlain, and is largely exposed at the 

 village of Chazy, the typical locality of the formation. This part 

 of the formation has not been identified west of Kingston, nor so far 

 east as Three Rivers. It lies therefore altogether within an area 

 of about two hundred miles in length by one hundred in breadth. 

 Outside of this area none of the Chazy Crinoids or Cystideans have 

 been discovered. 



Although for practical purposes it is most useful to treat of the 

 Chazy as a formation distinct from that of the Birdseye and Black 

 River limestone, yet the two deposits are most closely connected 

 zoologically, since we find that, out of seventy-five species, about 

 twenty, or more than one fourth, are common to both. 



Blastoidocrinus CARCHARiiEDENS, Billings. 

 Plate I. Figures la. In. 



Description. — Although the remains of the somewhat extraordinaiy 

 species for which the above name is proposed are exceedingly 

 abundant in the Chazy Limestone, and have for a long time attracted 

 the attention of geologists, yet no specimens have been collected 

 sufficiently perfect to enable us to make out the arrangement of all 

 the parts. Indeed, so remarkable is the form of the principal plates, 

 and so unlike any other fossils known in the Lower Silurian rocks, 

 that, until very recently, no one has succeeded in shewing how they 



