THE EARLIEST KNOWN VERTEBRATES 27 
been, by the drying up of this lake, penned into 
a pool about seventy-five feet long by twenty- 
five feet wide. ‘The fish were literally packed 
together like sardines, layer upon layer, and a 
shot fired into the pool would set the entire 
mass in motion, the larger gars as they dashed 
about casting the smaller fry into the air, a 
score atatime. Mr. Webster estimates that 
there must have been not less than 700 or 800 
fish in the pool, from a foot and a half up to 
_ seven feet in length, every one of which per- 
ished a little later. In addition to the fish in 
the pond, hundreds of those that had died pre- 
viously lay about in every direction, and one 
can readily imagine what a fish-bed this would 
_ have made had the occurrence taken place in 
the past. 
__ From the better-preserved specimens that do 
now and then turn up, we are able to obtain a 
very exact idea of the construction of the bony 
cuirass by which Pterichthys and its American 
cousin were protected, and to make a pretty 
accurate reconstruction of the entire animal. 
These primitive fishes had mouths, for eating is 
a necessity ; but these mouths were not associ- 
