IJyVEETEBRATE ANIMALS IN PALEOZOIC ROCKS. 



603 



• Two species have been recognized in the Potsdam Sandstone of 

 Canada and the United States, Scolithus linearis of Hall and 

 Sc. canadensis of Billings. The former is usually straight, at right 

 angles to the bedding, and smooth, or with obscure striation. The 

 latter is ratber smaller, tortuous, and unequal in diameter, sometimes 

 branching and curving, and occasionally showing slight transverse 

 ridges on the sides of the cylinders. 



The latter species is very abundant in the Potsdam of St. Anne's 

 on the Island of Montreal, where many varieties can be collected ; 

 but none of them shows any distinct structure. So far as indicated 

 by the ordinary specimens, they may be moulds left by the decay 

 of plants, sponges, or corals, or by the stems of Lingulce, or the 

 burrows of worms. 



rig. 7. — Slab with castings of Scolithus. Perth, Ontario. 

 (From a Photograph.) 



Their true nature is made evident by a fine slab kindly presented 

 to the Peter-Eedpath Museum by Mr.'W. J. Morris, of Perth, On- 

 tario. A portion of the upper surface of this slab is represented in 

 fig. 7, which shows rounded pellets and ridges of hardened sand, very 



Q.J.G.S. No. 184. 2x 



