106 CATALOG or FOSSIL FISHES IN THE MUSEUM 



Dermal Plates — -Gen. and sp. indet. 



(Text-fig. 37) 



Two fragments of plates in the collection, found in the Conodont 

 bed, at Eighteen Mile Creek, differ from all other ornamented plates 

 hitherto described and probably represent a new genus. They are 

 flat, 2 to 4 mm. in thickness, with one face perfectly smooth, and the 

 other ornamented with parallel, low, rounded ridges which gradually 

 diminish in diameter toward one side of the plate. Along one edge, 

 which is perfect, the smooth face of the plate (in both specimens) is 

 beveled to a knife edge, the beveled margin being 4 mm. in width. 

 The ornamented face, on the other hand, shows no beveling, the ridges 

 continuing clear up to the edge. The ridges make an angle of about 

 60° with this natural edge. 



Fig. 37. Fragiients Representing an Undiscovered Genus, Probably 

 Arthrodiean. Natural Size 



A, fragment with narrow ridges; E 2440. B, fragment with coarser ridges 

 E 2439. 



These fragments clearly indicate a form different from any hitherto 

 described. They may be compared only with Holonema plates, 

 although in the latter genus the ridges are very much finer and usually 

 broken in places into dots. The fragments appear so pecuUar that we 

 have even doubted whether they belong to fishes, but micro-sections of 

 them clearly show bone cells. 



It would, of course, be premature to name this form imtil at least 

 one complete plate is found. 



E 2439 A fragment 3 cm. in length (fig. 37B), bearing 8 low ridges 

 on the ornamented face. The broadest ridge is 4 mm. 

 wide, the narrowest about 2. 



