390 L. D. -Biivling — Protichnites and Cliinactichnites. 



and sank deeply into the bottom ; (^) the ends of the legs were 

 more or less pointed and conld only support the entire animal 

 when walking on a hard bottom {i may have been made by a 

 different animal) ; {j) the legs were not all of the same length ; 

 (k) the question of whether the median portion touched the 

 bottom or not was apparently one of whether or not the bot- 

 tom was soft enough to allow the legs to sink in, though it 

 must be recorded that the trail described in ^ is 6 inches or 

 more across and may have been made by a very large and per- 

 haps strong form ; [T) the front and back legs were respectively 

 shorter than those in the centre ; (m) in making this trail, g^ 

 the animal was apparently skipping along with the body sup- 

 ported in the water, and the impressions of the feet are proba- 

 bly not confused. If this inference is correct, and remembering 

 that the trails are crossed by others, the number of pairs of legs 

 was in all probability 6, though it averages nearly 7. 



Climactichnites. 



Logan, the first describer of these trails, believed them^* to 

 be the work of molluscs, a suggestion which received support 

 as late as 1903 when Woodworth'' published the first illustra- 

 tion of the peculiar oval bodies which have been found at one 

 end of the trails at Mooers, I^ew York. Walcott'^ has recently 

 figured a similar oval body from the Upper Cambrian at New 

 Lisbon, Wisconsin. He refers them to the work of annelids, 

 a reference which was anticipated by Gratacap in 1901.^^ 

 Curiously enough several of the earlier writers believed Climac- 

 tichnites and Protichnites to be different expressions of the 

 trail of the same animal, an observation which received experi- 

 mental confirmation at the hands of Sir William Dawson^Svho 

 discovered that when walking on the bottom the horse-shoe 

 crab used its legs and made a trail like Protichnites^ but that 

 in shallow water just covering the body it propelled itself by 

 moving its abdominal gill plates and left a trail resembling 

 Climactichnites^ (a) " except that the oblique furrows made by 

 the legs between the median and lateral ridges are directed 

 in the reverse direction ";'' (^) " except that in the track of 

 Limulus the lateral and median lines are furrows instead of 

 ridges.'"" Jones'' believed them to be the flattened galleries of 

 burrowing crustaceans, and Grabau^' in 1913 suggests that the 

 oval bodies of Woodworth ma3^ be collapsed burrows. Dana,^* 

 Billings,"* and Packard" believed they were to be ascribed to 

 trilobites. Todd"" concludes that the animal was provided 

 with a rigid caudal shield, with bristles or slender spines, and 

 that the ambulatory organs leaving the last impressions were 

 very perfectly flexible and must have been in pairs, each capa- 

 ble of motion independent of its fellow. Hall" says that "the 



