CANADIAN FOSSILS. 49 



I. Pleurocystites squamosus, Billings. 



Plate I. Figures la, Lb, Ic, Id. 



(Canadian Journal, vol. ii. p. 251, 1854; Geol. Survey of Canada, Report, 1856, p. 286.) 



Description. — In this species the large plates on the dorsal side are 

 smooth, or but slightly marked with obscure radiating and concentric 

 ridges, and the opening on the anterior side is protected by an 

 integument composed of a vast number of small, mostly hexagonal 

 plates, each less than the fiftieth part of an inch in diameter near 

 the border, and about the twentieth of an inch in the centre of the 

 space. The rhombs are small and somewhat elliptical, "the larger 

 axes of the upper two being transverse to the length of the fossil ; 

 in a specimen with a body thirteen lines in length the left upper 

 rhomb has a transverse axis of three lines and a vertical axis of two 

 lines in length. The rhomb on the right is two lines long and one 

 and a-half broad ; the basal rhomb is about of the same size as the 

 last mentioned ; they are all slightly elevated above the general 

 surface, and either flat or only a very little concave. The pores 

 extend completely across the rhomb from one side to the other. 

 The column is strongly annulated, and the projecting joints or rings 

 striated vertically, so that when well preserved they have a. nodulose 

 appearance. 



Explanation op Figures. Plate I. 



Figs, la and 16. Dorsal views of two specimens. 



Fig. Ic. Ventral view of a specimen shewing the plated integument and" strong borders 



formed by the folding over of the dorsal plates ; the mouth is at 0. 

 Fig. Id. Ventral view of the upper part of the cup and arms of a specimen of this 



species, the remainder of which is completely buried in the stone ; le is 



the same enlarged ; at a is the small sub-apical aperture. It is represented 



too large in the figure. 



Locality and Formation. — Trenton limestone, near the middle of the 

 formation at Ottawa. 



Collectors. — E. Billings, J. Richardson. 



II. Pleurocystites eobustus, Billings. 



Plate I. Fig. 2a. 



{Canadian Journal, vol. ii. p. 252, 1854; Geol. Survey of Canada, Report, 1856, p. 286.) 



Description. — In this species the rhombs are obscurely elliptical, 

 or rather in the shape of a spherical triangle ; they have somewhat 

 the appearance of a rhomboid, but then the angles are so much 



D 



