616 GEOLOGY OF OHIO. 



in length and its jaws are bnt three inches long. Liognathus, of Dr. New- 

 berry, is yet smaller. But the anterior part of the new species — the only 

 piece found — is five and a half inches long and indicates at least eight 

 inches as the total length of the mandible when perfect, that is to say, a 

 living Coccostens of about forty inches. This is in harmony with the 

 great size attained by the other species in late Devonian time. 



The mandible shows a row of eight blunt denticles on a raised part 

 of its upper edge in advance of the middle. In front and at the back of 

 these the edge is lower. The characteristic sj'mphysial teeth are present, 

 but have been broken so that only their bases can be seen. There are 

 three of these, as may be seen by an examination of the end view of the 

 mandible shown at a in figure 2. The number of these in Coccosteus 

 varies from five to eight. In Hugh Miller's figure six are represented, 

 though only five are spoken of in the description.* 



In writing of the mandibles of Dinichthys and Titanichthys (Monog. 

 p. 132), Dr. Newberry has likened them to that of Coccosteus. He says: 



"I found in the British Museum a number of jaws of Coccosteus in 

 which the form is essentially that of Dinichthys, viz., the anterior ex- 

 tremity is turned up and forms a prominent denticle and. the whole organ 

 is only a miniature copy of the mandible of Dinichthys Hertzeri." 



There is, however, no such resemblance between the jaws here de- 

 scribed and those of 'Titanichthys and Dinichthys. No indication of the 

 upturned tip forming a pointed tooth can be detected. Nor is any sem- 

 blance of such a structure shown in any figure of Coccosteus known to 

 the writer. The explanation of the confusing statement of Dr. Newberry 

 is given by Mr. A. Smith Woodward, in his "Catalogue of Fishes in the 

 British Museum," (p. 285, vol. II), where he writes: "This and the fol- 

 lowing specimens are probably reierred to by Newberry as closely resem- 

 bling the mandibular rami of Dinichthys. The beak-like appearance, how- 

 ever, is entirely due to the accidental flaking of the bituminous substance 

 into which the fossils are converted." 



The Sharks of the Cleveland Shale. 



But these gigantic Placoderms or armor-clad fishes were not the only 

 denizens of the ancient sea of Ohio. If they dominated the muddy bot- 

 tom where the black shale was accumulating as do the mud-fish of the 

 present day, yet above them in the clearer water swam sharks of various 

 forms and sizes. Between them these two groups probably divided the 

 empire of the sea. 



We as }*et know only a few of the latter group. The labors of Messrs. 

 Fyler and Kepler, and especially later of Dr. Clark, have brought to light 

 several specimens, the first of which were figured in the Monograph by 

 Dr. Newberry under the names of Cladodus Kepleri and of C. Fyleri. 



* Old Red Sandstone. 



