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 hke 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 at a time. ^Ir. 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- 



