ISOSPOKDYLI. 69 



neo, etc., and 0. leichardtii Gthr., in New Zealand, all in the southern hemis- 

 phere, or near the equator. Two other genera, Vastres and Heterotis, have 

 been associated with it, and these belong to the same hemisphere, or to those 

 faunae which characterize it, in their extensions north of the equator. It is, 

 therefore, interesting to note that the first representative of the type found 

 in any of the northern faunal regions, belongs to an age evidently Eocene. 



Our first knowledge of this family and genus as it occurs in North 

 America, was based on a fragment of shale from the railroad cut at Green 

 River, Wyoming, which bears part of the scales of one side of the body 

 of the fish. The specimen is without any portion of the head or fins. In 

 consideration of the structure of the scales I was induced to refer the 

 species to the genus Osteoglossum. The next addition to our knowledge of 

 this form was furnished by Dr. Leidy, who gave a brief description of 

 portions of the jaws supporting teeth, of a species found in the Bridget 

 foi-mation. This fish he termed Pliareodus acutus. No diagnosis of the 

 genus was given, nor were any grounds for creating it assigned. I have 

 not, therefore, been able to use the name. Subsequently I attempted to 

 •define the genus thus named by Dr. Leidy,* inadvertently writing it Phare- 

 cdon. The specimens of jaws then in my possession were found by myself, 

 mingled with the bones of Rhineastes, and it was from the latter that my 

 diagnosis was drawn up. Phareodon Cope must then be regarded as a 

 synonym of Rhineastes, and as it had its origin in error, naturalists will 

 probably agree with me in sinking it altogether. 



Four species of this genus are enumerated in the following pages, but 

 I am not able to give the distinguishing characters of three of them. It is 

 probable that the D. acutus Leidy is distinct from the other two, which have 

 been found in the Green River shales, but as only its jaws are known, 

 these offer but few characters. At present the type specimen of D. encaustus 

 remains considerably larger than any of those of the D. testis, which have 

 been found, and comes from a locality distant from whei'e the latter is found. 



• Annual Report U. S.Geol. Surv. Terrs.,1872 (1873), p. 637. 



