248 NORTH AMERICAN INDEX FOSSILS. 



the successive packings of sand, in the making of successive bur- 

 rows one above the other. The form is J-shaped. Ordovicic- 

 Siluric. 



yy. D. archimedes (Ringueberg). Siluric. 



Flat, turreted or spiral plates of sandstone standing vertically 

 in the enclosing rock and often twelve to fourteen inches in depth, 

 rarely more than four inches wide and one half inch thick; marked 

 by J-shaped lines and ridges. 



Medina sandstone of New York; Tuscaroraof Pennsylvania, etc. 



XX. Climactichnites Logan. 



Trails marked by median and two marginal ridges, and by trans- 

 verse, broad groove, or, in solid molds, by median groove and 

 transverse, broad ridges, the transverse elements converging ob- 

 liquely to the longitudinal ones. Cambric. 



78. C. wilsoni Logan. Cambric. 

 Large, the width measuring from five to six and one half inches ; 



transverse grooves about one inch, as measured from crest to crest 

 of dividing ridge. 



Potsdam sandstone of New York and Canada. Other species 

 occur in the St. Croix of Wisconsin, etc. 



This trail has been generally regarded as that of some crustacean. 

 It may have been made by some unknown terrestrial or semiter- 

 restrial animal. (See J. B. Woodworth's paper cited above.) 



XXL Taonurus Fisher-Ooster. 



{Spirophyton Hall.) 



Thin plates of ridged sand rock, nearly horizontal, U-shaped, 

 suboval, or irregularly lobate, or more rarely forming low-inverted 

 spirals, with the larger volutions downward; both faces of plates 

 marked by U-shaped or otherwise curving, parallel lines. Origi- 

 nally regarded as a plant, also interpreted as mechanical markings 

 by basally attached plants moved by wind; interpreted by Sarle 

 as packings of successive burrows similar to Dcedalus. Cambric- 

 Tertiary. 



79. T. caudagalli (Vanuxem). (Fig. 1540.) Devonic. 

 In form resembling a rough spiral suggesting the outline of a 



rooster's tail. 



