244 MM. Pictet and Humbert on the Fossil Fishes 



there are, however, the two principal types. Sharks and Rays. 

 These fishes are for the most part difficult of comparison with 

 other fossil species ; for, in most deposits, the Elasmobranchi are 

 only indicated by isolated teeth : in the Lebanon, however, the 

 case is quite different ; there are no isolated teeth, but some few 

 entire bodies. 



The subclass of the Ganoids is, in all known faunas of the Cre- 

 taceous period, in rapid course of extinction. This renders all 

 the more interesting the fact that the faunas of the Upper Jura 

 which immediately preceded this period are rich in numerous 

 and fine characteristic species of this subclass. We have not 

 found at Lebanon any true Ganoid ; for we no longer retain in 

 that subclass the order Hoplopleuridse established by one of our- 

 selves. This order belongs properly to the great series of Te- 

 leosteans. 



This third subclass is consequently by far the most important. 

 It afibrds almost the total of the fauna, and it is with it that we 

 have more particularly to deal at present. 



As we have said above, M. Agassiz did not place the existence 

 of the Teleostei further back than the Cretaceous period ; the 

 greater number of authors now, however, recognize an exception to 

 this rule, and regard as Teleosteans in all probability the genera 

 Tharsis, Leptolepis, &c., with minute rounded scales. Taking 

 for granted the correctness of this view, which it would take us 

 too long to discuss here, we have to notice a very important 

 fact, which is that the Teleostean fishes of which M. Agassiz 

 forms his family Halecoides, and which we know under the 

 names of Salmones and Clupea, are manifestly the nearest rela- 

 tives of these same Jurassic genera. The numerous family to 

 which these precious types of our present seas belong are actu- 

 ally the descendants of the Jurassic Teleosteans. They have a 

 history longer than that of any other existing family, and may 

 be regarded as, in some sort, the trunk of the genealogical tree 

 of the fishes of our present seas. 



It is, further, very interesting to find that these fishes are 

 the ones which present developed in the highest extent the 

 normal characters of their class, and that they thus in some 

 sort represent the archetype thereof. A theoretical anatomist, 

 wishing to set forth this archetype, would be inevitably led to 

 depict a figure almost exactly like that of a Halecoid, since he 

 would assign to it ventrals in the normal position far back on 

 the abdomen, and a mouth with the edge composed of both 

 maxillary and intermaxillary ; and nothing is more normal than 

 the fins of a salmon and its regular and fusiform body. 



We may, then, assume that the most ancient Teleostean 

 fishes were the most normal in their forms, and that their cha- 



