406 C. R. EASTMAN — JURASSIC FISHES FROM BLACK HILLS 



to tlie other. The paleontologic evidence is entirely in accord with Mr 

 Darton's determination of the horizon as basal Jurassic. 



Description of fragmkntary Fossils 

 amiopsis(?) dartoni sp. nov.* 



Plate 48, figures 1, 2. , 



Associated with the preceding species are numerous fragmentary re- 

 mains, indicating fishes of large size, with powerful fins and delicate 

 cycloidal scales. Although vertebral centra have not been observed, the 

 presence of stout ribs suggests a well ossified vertebral column. No head 

 bones beyond those shown in plate 48, figure 1, exist in the collection, 

 and the only clue as to systematic position is the decidedly uncertain 

 one afforded by scale characters. These point tp a place among the 

 Amiidse, 



The scales are covei'ed superficially with a very thin coating of ganoine, 

 their contour is almost perfectly elliptical, and they appear to have been 

 deeply overlapping. The major axis of the ellipse, which was presum- 

 ably longitudinal, measures about 1 centimeter in the larger scales. A 

 number of them are to be seen, although rather indistinctly, in the lower 

 part of figure 1, and an enlarged drawing is given of a detached scale in 

 figure 2 of plate 48. In the upper part of figure 1 may be recognized the 

 right and left clavicles and a large semicircular operculum, not unlike 

 that of the recent Amia. The large pectoral fin, with curved, distally 

 articulated rays to the right of the operculum, is still attached to a part 

 of the clavicle, broken oS" from the upper portion. In line with the 

 pectoral below lies the pelvic fin ; below and to the left is seen one of 

 the unpaired appendages, possibly the anal fin, overlying which at one 

 end is a rib and at the other the anterior margin of the opposite pectoral. 

 There are no fin-fulcra. 



It is greatly to be hoped that further material may be discovered which 

 shall elucidate the structure and relationships of the form here so ob- 

 scurely represented. There exist as yet only slight grounds for assum- 

 ing a relationship with Megalurus, Amia, etcetera, much less for institut- 

 ing comparisons with them. If Correctly referred to the Amiidse, the 

 present occurrence extends the range of this family at least as far back 

 as the Lower Jura, whereas hitherto it was supposed to have been in- 

 itiated in the Upper Jura. At all events it is interesting to know now, if 

 we can know no more, that the two groups of rhombic and thin cycloidal 



. *The specific title is given in honor of Mr N. H. Dartou, who discovered all the remains de. 

 $cribed in this paper. 



