TRACKS 01' INVERTEBBATK ANIMALS. 23 



the anterior pair a and h, and the corresponding pair b 

 and c in fig. 4, is exactly i-^ of an inch. There is no 



trace of any defined median vertical line^ but there is 

 a distinct elevation in each of the areas separating the 

 parallel curved grooves, and the vertical median line 

 between each two rows is also faintly raised, as if, in the 

 latter case, a slight concavity existed at the corresponding 

 part of the living animal. What that creature may have 

 been is more than doubtful. Except what appears in the 

 successive octants, no continuous trail of any kind appears 

 on the slab, making it obvious that the creature possessed 

 no Trilobite-like tail or sternal ridge. The object may 

 safely be placed in the genus Protichnites , and be distin- 

 guished as P. Davisi, after my friend J. W. Davis, Esq., 

 F.G.S., of Halifax, by whom the specimen was found, and 

 who has kindly allowed me to describe it in this memoir. 



Leaving these two relics of a past age, I would now 

 direct attention to some phenomena of modern origin, 

 which I have recently observed on the sea-shore. Two 

 summers ago my attention was arrested by some remark- 

 able appeai'ances on the sands left bare by the retreating 

 tide at Llanfairfechan in North Wales. Watching the 

 formation of these appearances, it soon became obvious 

 that they were formed by small drainage-streams flowing 

 either towards the sea or towards large temporary depres- 

 sions in the sand running more or less parallel with the 



