TRACKS OF INVERTEBRATE ANIMALS. 21 



tenths of an inch; usually, however, they fall short of this 

 depth. A median furrow runs along the entire length of 

 the track in these casts, representing some median abdo- 

 minal groove in the living organism. Numerous parallel 

 ridges and alternating furrows proceed outwards, down- 

 wards, and backwards (?) from this groove, about ten such 

 ridges occurring in each lineal inch. Along the summit 

 of each of these lateral ridges we have a row of small 

 tubercles, about twenty to an inch. These tubercles 

 sometimes appear to be the summits of obtuse elevations 

 which pass obliquely down one side of each ridge, disap- 

 pearing as they reach the median line of the contiguous 

 furrow, the opposite side of which presents no such 

 appearances. These small sculpturings suggest that the 

 appendages (legs ?) of the animal to which the primary 

 and secondary ridges and furrows are due had serrated or 

 crenulated margins. Fig. 2, Plate III., represents the 

 arrangements in question diagraramatically, the appear- 

 ances being made rather stronger than in reality to illus- 

 trate their general features. 



The surface of the slab (fig. i) is covered with parallel, 

 rounded ridges and furrows of varying depths and eleva- 

 tions. These may represent drainage- lines, but they also 

 suggest somewhat strongly the idea of a wind-blown 

 surface of sand. 



Fig. 3 represents a second fragment, in which the lateral 

 ridges and fun'ows of one of the two tracks are less 

 uniformly regular, some of them being stronger than in 

 the case of fig. i ; but here again the track is connected at 

 the end on its right with an irregular boss, representing a 

 corresponding depression on the primaeval beach. 



These objects correspond closely to those supposed 

 vegetable organisms to which Schimper has assigned the 

 name of Chrosfiocorda. Though I am altogether unable 



