272 PROCEEDINGS OF THE NATIONAL MUSEUM vol. i08 



II. B.eassignment of Petalolepis? fibrillatus Cockerell 



Plate 2 



The generic name Petalolepis first appeared in an unpublished 

 catalog of fish remains from the upper Cretaceous Planer formation 

 of Saxony, Germany, compiled by Prof. Moritz Steinla. Sub- 

 sequently in formal description, Geinitz (1868) considered Petalolepis 

 a synonym of the elopid genus Osmeroides (Agassiz, 1844) and proposed 

 the name 0. divaricatus for the identical Steinla specimens. Cockerell 

 (1919, p. 173) interpreted the same scales as those of an albulid fish, 

 and finding the name Petalolepis available for the reception of the 

 hence reassigned divaricatus species, provisionally referred a new 

 American species, fihnllatus, to the generic term. Heretofore known 

 only by the one holotypic specimen (USNM 8662), two additional 

 scales of Petalolepis? jihrillaius were recently recognized among the 

 national collections of fossil fishes. 



The variety and individuality of fish scales have been amply 

 demonstrated through the work of many investigations in all parts 

 of the world. However, when attempts have been made to arrange 

 these exoskeletal elements in developmental series, the resultant 

 trends of structural variation, either parallel, convergent or divergent, 

 appear to cross phylogenetic lines. In direct consequence, serious 

 doubts are entertained by many ichthyologists not only of the ability 

 but also of the use for identifying and naming fragmentary remains 

 of such parataxial nature. Although disassociated fish scales probably 

 never can constitute a completely satisfactory base for precise studies 

 of broad scope, the future clarification of group relationships and 

 corresponding refinement of fish classification, coupled with accumu- 

 lated factual data concerning development at all ontogenetic and 

 phylogenetic levels, wHl correct many of the difiiculties surrounding 

 the use of scales. Within restricted limits, on the other hand, scales 

 have been proved effective tools. In the present case a new definition 

 of Petalolepis? jihrillatus seems justified. The fossil specimens are 

 entirely distinctive in fundamental structural characteristics and are 

 not to be identified with the genotypic Petalolepis divaricatus (Geinitz) 

 from Germany. Equally important, they are of potential strati- 

 graphic utility as representative of practically unknown marine faunas 

 from near shore and lagoonal environments for a seemingly short 

 interval of the late upper Cretaceous in North America. 



Grateful acknowledgment is offered Dr. R. W. Brown, Dr. Lore R. 

 David, and Mr. Shelton P. Applcgate for advice and various other 

 aids. The photographs accompanying this note are the work of 

 Mr. Jack Scott, Department of Geology, U. S. National Museum. 



