338 ILLINOIS STATE ACADEMY OF SCIENCE 



But it is the fish life that most concerns one, and it pre- 

 supposes many other forms of life on which the fish sub- 

 sisted, but whose remains may have been too soft to have 

 been preserved. Still there are numerous marks and 

 tracings on the slate which seem to reflect a multiplicity 

 of forms, and not the least of these are what are presum- 

 ed to be the teeth of mollusks. 



One Thanksgiving day a number of years ago I split 

 open a slab of this slate about two feet square and was 

 about to strike it again when my attention was attracted 

 by a row of sharp teeth along extended jaws or mandi- 

 bles. At the same time there appeared over the surface 

 of the slab a series of bones still showing the bony struc- 

 ture, and from them ran what seemed a short segment of 

 the backbone. Stout spines, two or three in number, were 

 back of the jaws some distance. The teeth were keen 

 pointed and less than half an inch in length, with denti- 

 cles each side extending up from the base of the tooth. 

 Some of these teeth showed a curvature backward. 



I sent the specimen to Professor Cope, then a recog- 

 nized authority on fishes, and he became greatly interest- 

 ed in it, as it threw some light on controverted points re- 

 garding ancient fishes. He made the specimen, which he 

 described as that of a paleozoic shark, the subject of a 

 scientific description in a work that he was then getting 

 out. Judging from the size of the jaws and the connect- 

 ing bones of the skull, it was a shark of considerable size, 

 and considering the teeth and their extreme sharpness, 

 was capable of doing much execution on the other deni- 

 zens of the water. Such backward curved teeth surely 

 gave it ability to hold what it once gripped. 



At the same time I sent Professor Cope another type 

 of fish from the same formation, but evidently of differ- 

 ent habits and adapted to other forms of food. It ap- 

 peared to be somewhat reptilian in shape , with its long 

 narrow head and the extension backward of the jaws. 

 But its mouth was filled with crushing or pavement teeth, 

 that is, teeth rounded on top with a raised center and 

 somewhat corrugated. The dentition was thus in sharp 

 contrast to that of the shark previously described. From 

 the general appearance one would judge that this crea- 



