CANADIAN FOSSILS. 



If a section be made passing through the ambulacral orifice, the 

 mouth and base of a specimen of this species, it will exhibit the 

 following arrangement of the orifices : — 



In the above fig. 1, ?« is the place of the mouth, aa the anterior 

 arm, o the ambulacral orifice, ])a the posterior arm, c the column, 

 as the anterior, and 'ps the posterior side. Fig. 2 is a diagram of a 

 specimen seen in the direction of the line oh of figure 1, shewing 

 the arrangement of the arms in two half-circles, one of which is 

 between the mouth and the ambulacral orifice, the other being on the 

 opposite side. 



The mouth of this species being five-sided, was probably provided 

 with valves. It is one line in diameter, and is therefore more than 

 four times the area of the ambulacral orifice, which has a length 

 of less than half a line. 



Some small specimens in the collection shew that when young this 

 species was of an oval or pyriform shape. 



Dedicated to M. J. Barrande of Prague, Bohemia, author of 

 " Systeme Silurien du centre de la Boh^me," &c. &c. 



Explanation of Figures. Plate VII. 



Fig. 2a. View of the left side of a specimen ; a, the arm. 26. Posterior view of the same. 

 2c. Anterior view of another specimen. Id. The arm of la magnified, 

 shewing the short branches of the ambulacral furrow to the bases of the 

 pinnulae. 



Locality and Formation. — Chazy limestone, near the city of 

 Montreal. 



Collectors. — E. Billings and J. McMullen. 



Genm Pal^ocystites, Billings. 



Generic Characters. — The body is oval or piriform, composed of 

 numerous plates, which are poriferous; the pores penetrate the 



