246 NORTH AMERICAN INDEX FOSSILS. 



Worm Burrows (systematic position doubtful). 



XV. ScoLiTHus Haldeman. 



Tube free, cylindrical or subcylindrical, vermiform, never 

 branched. Cambric-Ordovicic. 



71. S. linearis Hall. (Fig. 1539.) Cambric. 



Surface nearly smooth, sometimes apparently striated ; form 



f 



Fig. 1539. Scolithus linearis, the pencil-like filling of the burrow. (After Walcott.) 



rigidly straight; diameter one eight to one half inch; length from 

 a few inches to several feet. 



Upper Cambric of New York, Newfoundland, Vermont, Massa- 

 chusetts, Pennsylvania, Tennessee, etc. Other species distinguished 

 according to the size of the tube are: y2, S. canadensis Billings, 

 and 73, S. minutus Wing ; the first Upper Cambric, and the second 

 Lower Ordovicic. 



XVI. Arenicolites Salter. 



Circular holes, generally in sandstone, occurring in pairs and 

 resembling the burrows of the modern Arenicola. Cambric. 



