406 University of California PubUcatiohsi [.Gtaoiioor 



of this paper. The principal fossil flounders have been obtained- 

 from the Eocene and Miocene beds of Europe and nearly all of 

 them have been referred to the genus Rhomb lis, of which Rothus 

 is an older name. Both us miniums is the oldest known species, 

 having been described by Agassiz from the ' Eocene of Monte 

 Bolca. The other nominal species, mostly Miocene and known 

 from fragments only, are closely related to this. The fact that 

 these fragments belong to the general type of the turbotand 

 brill (Psettinae) has led to the supposition that this was the 

 primitive type of the flat-fishes. The halibut tribe Hippoglos- 

 sinae are less specialized, but as Jordan and Evermann observe, 

 "The primitive simplicity of the halibuts may be due to degen- 

 eration." To this date no Hippoglossinae have been found fossil, 

 nor have any of the small-mouth forms ( Platessinae) 1 which, are 

 supposed to be derived from the Hippogiossinae, except in very 

 recent rocks. 



It is believed that the specimen described here may be found 

 to be of great significance in this matter, as it is apparently a 

 primitive representative of the halibut tribe, being more gener- 

 alized than Both us minimus, as well as vastly larger in size than 

 that diminutive species. 



The identification of the bounders will doubtless rest largely 

 upon skeletal differences such as : the degree of approach to 

 symmetry; the insertion of the ventral fin; the simplicity, 

 number, and strength of the vertebrae; the relative size of the 

 head and body-cavity ;: the position of the eyes; the strength of 

 the bones; the number and relation of the spines to the inter- 

 spinous bones; the character of the fins and the number of their 

 rays ; the presence and character of the teeth and the length 

 and direction of jaws, etc. In considering these points several 

 problems suggest themselves, among which are (a) whether the 

 earlier flounders had a large or small mouth; (b) whether they 

 had large teeth or small; (c) whether they were "right" or 

 "left-handed" forms; (d) whether they resembled the halibuts 

 more than they did the brill or the turbot ; (e) what was their 

 habitat; (/') ami what kind of a form should be looked for as 

 the common ancestor of both soles and flounders, for two species 

 of sole are also found in the Miocene of Europe. 



