2 Early Trilobites of the Cambria7i <Rocks — Matthew. 
branching organisms resembling seaweed and about one hun- 
dred feet higher a remarkable track occurs which is also found 
in the oldest Cambrian rocks of Sweden. This was named by 
Dr. Otto Torell ArejiicoUtes gigas^ which n.^me he afterward 
changed to Psanujiichnites gigas. Although he at first 
thought this track to have been made by a worm he afterward 
demurred to the absolute reference of such trails to the An- 
nelida, remarking that both molluscs and crustaceans made 
similar marks on the sand. But no gasteropods except minute 
species are known in these ancient rocks, and there is such a 
variety of trilobites both for size and form in the Acadian series 
to which Psammichnites extends that the trilobita do not seem 
likely to have given origin to a track so unchanging in size and 
wdth such features as this possesses. 
Psammichnites is most^probably the track of it gigantic ma- 
rine worm. The centre is moderately dejDressed and there is 
the same tendency to make little ridges on each side of the track 
when passing over the raised part of ripple-marked sandstones 
and to throw casts (of the intestmal canal?) in the hollows or 
depressions between the ridges, which may be observed to 
characterize the operations of worms on the sea shore at the 
present day. The track however, differs from ordinary worm 
trails in its directness, running almost straight for many inches 
and sometimes for the distance of a foot, and deviating from the 
straight line only in long open curves. As it lacks the sinuous- 
ness of the ordinary worm track, the animal that made it may 
have had perceptiv^e organs to guide it on its course, differing 
from those of ordinary worms. 
The track is about three-quarters of an inch wide and is of ten 
marked by a groove or depression in the middle, as in Cruziana. 
Apparently the same track is found in the Acadian series near 
its base where the casts that accompany it occasionally contain 
shells of brachiopods (Z?««ar.y£)«/a) pteropods {^Diplotheca) and 
tests of trilobites [Agraulos, <£-c.). Whether these are acci- 
dental enclosures, or have passed through the intestinal canal is not 
clear, but the latter view seems more probable. This fossil 
track serves to link the two series and shows with other biologi- 
cal features that the lower, as well as the upper series, is of 
jCambrian age. 
