52 CANADIAN FOSSILS. 



the latter with the portion of the basal rhomb of P.Jilitextus, repre- 

 sented in la, the difference will be at once detected ; all the others 

 are more or less distorted. In P.Jilitextus the left upper rhomb is a 

 little more than one-third the length of the body, but in P. elegans 

 it is a little more than one-fourth. The plates of the ventral side 

 have not yet been seen. 



Explanation op Figures. Plate II. 



Pigs. 2a, 2&, 2c and 2(11 are dorsal views of this species. It is doubtful whether 2d 

 should be referred to this species or to the thickly striated varieties of 

 P.Jilitextus. The crushed condition of this, and indeed of all the specimens, 

 renders it most difficult to decide when the species are so closely allied. 



Locality and Formation. — Trenton limestone, City of Ottawa. 

 Collector. — E. Billings. 



V. Pledroctstites exornatus, Billings. 



Description. — Rhombs sub-triangular, surrounded by a thin sharp 

 border, which is a good deal elevated above the surface. The upper 

 side of the rhomb is nearly straight, and the other two sides converge 

 to a slightly rounded angle below. The outline of the rhombs of 

 this species is like that of P. rohustiis ; but, on the other hand, the 

 poriferous area or portion has a flat surface, while in the other species 

 it is concave. The plates of the ventral integument are about the 

 size of those oi P.Jilitextus, from which species it differs by the form 

 cf the rhombs ; the size of the ventral plates also separates it from 

 P. squamosm. The column is beautifully striated longitudinally. 



Locality aiid Formation. — Lower part of the Trenton limestone, 

 Montreal. Fragments resembling this species occur in the Chazy 

 limestone near Montreal. 



Collector. — E. Billings. 



VI. Pleurocystites Anticostiensis, Billings. 

 Plate I. Figure 3. 



{Geological Survey of Canada, Report, 1856, p. 288.) 



Description. — All that can be said about this species is that the 

 rhombs are very long and narrow, and the large joints of the column 

 so coarsely striated that they appear to be nodulose. Only a frag- 

 ment, consisting of a portion of the column and the lower part of 

 the body, has been collected ; the specimen measures eleven lines 



