90 CATALOG OF FOSSIL FISHES IN THE MUSEUM 



Dinomylo stoma sp. [Juvenile] 



(PI. 23, fig. 2) 



E 2042 A small left mandible on a piece of shale, shown in outer 

 view. Length, 42 mm. This is the smallest Dino- 

 mylostoma mandible ever found, and probably represents 

 a juvenile individual. 



Rhinestreet shale (Portage) ; Sturgeon Point, on shore 

 of Lake Erie, N. Y.; collected by Mr. F. K. Mixer. 



Dinomylostoma ? 



(PL 27, figs. 5, 6. — Upper Dental Plates) 



E 1859 and E 2398 There are two remarkable dental plates in the 

 collection, from the Conodont bed at Eighteen Mile 

 Creek, which differ from all other Arthrodire specimens 

 known to us. They are apparently upper dental plates. 

 From the presence of a laf ge tubercle on the worn surface, 

 (especially well shown in one of the specimens), and the 

 fact that one of the lateral margins falls abruptly away 

 from the wearing surface, somewhat as in a myiostomid 

 dental plate, we are inclined to the view that the two 

 elements are of the same kind, that is, upper dental plates 

 of a myiostomid. And in fact, it is probable that they 

 belong to one of the species of Dinomylostoma described 

 above. The reasons for this view are chiefly these : ( i) One 

 may expect to find the upper dentitioji in the formation in 

 which mandibles of the dinomylostomids are found, 

 particularly so as the upper dental plates are compact 

 and would stand an even better chance of preservation 

 than the mandibles. (2) These elements, especially the 

 one shown in Plate 27, figure 5, may be compared in a 

 general way with a myiostomid upper dental plate. (3) 

 Since in the mandible of Dinomylostoma the fimctional 

 margin is excavated, one would expect that the apposing 

 dentition would be convex, and this is the case with the 

 present elements. So that, taken all in all, there is 

 ground for believing that the two elements belong to the 

 upper dentition of Dinomylostoma. 



