1874.] J--^*^ [Cope. 



of the comet with that of the meteor, and remembering the prodigious 

 velocity of the former, may we not well imagine that its collision with 

 the highly attenuated upper atmosphere of the sun might develop latent 

 heat sufficient to enable it to rival the sun itself in splendor ? 



Although much of the evidence presented in favor of the existence of 

 "latent heat of expansion," and of its agency in the production of lumi- 

 nous phenomena, may be said to be circumstantial only, — I trust that it 

 will be found sufficiently cumulative, and accordant throughout, to enti- 

 tle it to examination. 



Philadelphia, March 25th, 1874. 



ON THE PLAGOPTERIN^E AND THE ICHTHYOLOGY OF 



UTAH. 



By Edward D. Cope, A.M. 



Bead iefore the American PMlosopliical Society, March 20th, 1874, 



The observations recorded below are based on the collections made by 

 the naturalists attached to the United States Geological and Topographical 

 Survey west of the 100th meridian, under direction of Lieutenant Geo. 

 M. Wheeler, and are published by permission of that officer. To Dr. 

 Henry C . Yarrow, in charge of the department of zoology, and to A. W. 

 Henshaw, assistant, the survey is indebted for matejial more fully 

 illustrating the character and distribution of the cold blooded vertebrata 

 of the valleys of the Colorado River and of Utah than any heretofore 

 brought together. As one of the results derived from a study of it, it 

 appears that the basin of the Colorado River is the habitat of a small 

 group of fishes of the family Cyprinidse, which may be called the Plagop- 

 terincB, which embraces three genera — Plagopterus, Cope; Lepidomeda, 

 Cope; and Meda, Girard. The group differs from others of the family in 

 the possession of two strong osseous rays of the dorsal fin, the posterior 

 of which is let into a groove in the hinder face of the anterior without 

 being coossified with it, thus constituting a compound defensive spine. 

 The rays of the ventral fin, excepting the first and second, are similarly 

 modified. The greater pai-t of their length consists of an osseous dagger- 

 shaped spine, with grooved posterior edge, which overlaps the border of 

 the succeeding ray, when the fin, like a fan, is closed up. The articulated 

 portion of the ray either emerges from the groove below the free acute 

 apex of the spine, or appears as a continuation of the apex itself. It is 

 worth observing that the only other instance 'of this ossification of the 

 ventral rays is to be seen in the extinct family of the Saurodontidce, of the 

 cretaceous period, the nearest approach among recent fishes being the 

 internal spine in the ventral fin of Amphacanthus. The dentition and 

 intestine of these fishes show them to be of carnivorous habits. Interest 



A, p. S.— VOL. XIV. Q 



