INYEKTEBKATE ANIMALS IN PALJilOZOIC EOCKS. 



601 



Pig. 5. — a^ Protichnite-like ; 5, Climactichnite-like Trails of 

 Limulus 2)olyplumus. Modern. Coast of Maine. 



referred certain transverse linear impressions with a broad central 

 groove from the Lower Carboniferous of Horton, which occur at 

 that place under different modifications, and sometimes seem to- 

 change into light scratches, or touches of feet employed in swimming, 

 or end abruptly, as if the animal had suddenly risen from the bottom.- 



Nathorst * and Bureau have further shown that impressions 

 similar to Bilohiies may be produced by the successive strokes of the- 

 tail of certain Crustaceans {Crangon and Palcemon). Prom all the 

 phenomena attending the Potsdam Climactichnites, I am now in- 

 clined to regard them as of this nature, and as implying the existence- 

 of a large Crustacean with a truncated tail divided into two movable- 

 lobes. This would account for the ridge sometimes dividing the 

 furrows and transverse ridges, and for its change of position from^ 

 side to side of the mesial line, — also for the interrupted ridges on 

 each side of the trail, which would be the natural result of the suc- 

 cessive strokes of a flat organ, — and for the appearances presented! 

 when the tracks turn abruptly t (see fig. 4). 



There is confessedly some difficulty in separating the marks knowns 

 as Phymatoderma from Pucoids allied to Caulerpa^ and even from- 



* Trans. Roy. Acad. Sweden, vol. xviii. no. 7, 1881. 



t "Impressions of Aquatic Animals," * Amer. Journ. Sci.' ser, 3, vyDl. v.- 

 1873, p. 16. 



