PALEOZOIC TIME — CAMBHIAN. 



479 



from the Potsdam sandstone of Keeseville, N.Y., the total length being a 

 fourth of an inch. The track, 51 inches broad, Fig. 586, from Perth, Canada, 

 described by Logan, has been referred to a large Trilobite, on the view that 

 the limbs of the species were natatory; and on 587 is a similar track, 4} 

 inches broad, from 'New Lisbon, Wis., besides a still smaller kind. The 

 partially natatory character of the limbs has been recently established by 

 Beecher (page 512). 



583-588. 

 583. 585. 586. 



Tbixobites. — Fig. 583, Dicellocephalus Minnesotensis (J) ; 584, D. lowensis (1) ; 585, Ptychoparia (Cono- 

 coryphe) minuta, head shield (4); 585 a, same, pygidium (4). Tracks. — Fig. 586, Cliraactichnites 

 Wilsonl, supposed to be those of a large Trilobite (f) ; 587, Climactichnites Youngi (the larger track), 

 with C. Foster!, the smaller; 588, Protiehnites septemnotatus. Fig. 583, 584, from D. D. Owen; 585, 

 585 a, F. H. Bradley; 586, 588, Logan; 587, Chamberlin. 



The tracks, a portion of the series of which is represented in Fig. 588, 

 were described by Owen from specimens found in the Potsdam sandstone of 

 Canada. The breadth of the pairs of tracks was six to seven inches. What 

 made them is not yet known. 



Besides the kinds of fossils mentioned above, there are also various markings and im- 

 pressions that are not fully explained. Among these are impressions 4-sided, 5-sided, 

 and circular in form, from Olenellus beds, which have been referred, first by Nathorst of 

 Sweden, and later by Walcott and others, to Hydrozoans or Medusae of large size. Tlie 



