THE DYNASTY OF FISHES. 237 



stone of New York, Canada, Ohio, and Michigan. If you 

 wish the name, here it is: " Machcer"-a-can f -thus, or "Dag- 

 ger-spine." 



Another type among the earliest American fishes was 

 (Rhyn'-cho-dus, or " Beak-tooth ") a form related to the Chi- 

 mce'-ra, which also resembles sharks. It has, however, a long, 

 whip-like tail; its gill-slits are covered by a flap of skin, and 

 the skull is blended with the jaws. The teeth consist of mi- 

 nute denticles firmly massed together into large tabular plates 

 which are inseparably blended with the jaws. It has a long 

 and powerful spine in front of each dorsal fin. The only 

 known specimens of Rhyn'chodus are found in the Cornifer- 

 ous Limestone of Ohio ; but it must have had a much wider 

 range. 



Another of the most common and most striking fishes of 

 the same age appears to have been a relative of the modern 

 sturgeons a family of plated Ganoids. Our American geolo- 

 gists have almost buried it under a pile of nomenclature, 

 which they have finished in the following shape : Mac-ro-pet- 

 al-ich'-ihys or "Big-plated fish." These fishes were of large 

 size. The cranium was composed of large polygonal plates, 

 united by double sutures which are nearly concealed by the 

 tubercled enameled surface ; the tubercles are stellate ; the 

 surface is ornamented by double rows of pores and single 

 thread lines, forming a pattern which does not correspond 

 with the plates below. These large, geometrically formed 

 plates often attract the attention of quarrymen, since they 

 are sometimes fifteen inches in length. 



In this assemblage of oldest American fishes, we have to 

 mention one more. This is a ganoid by the name of 0-nych'- 

 o-dus or "Hook-tooth." It was of large size. The cranium 

 was composed of a large number of bony plates covered with 

 an enameled and tubercled surface. The borders of the jaws 

 were set with a row of conical, acute, more or less recurved, 

 teeth ; and, in the middle of the lower jaw in front, was a 

 single series of large, curved, conical teeth, presenting a strik- 

 ing appearance, and often found imbedded in the Corniferous 



