400 



C. K. EASTMAN JURASSIC FISHES FROM BLACK HILLS 



Scales thick, rhombic, slightly over- 

 lapping, rugose or crennlated on poste- 

 rior half of each scale on part of the 

 body; principal fiank scales rarely, and 

 then only in part, deeper than broad, 

 several series of ventral scales much 

 broader than deep ; no enlarged scales 

 on dorsal ridge nor in vicinity of anus. 



Lateral line inconspicuous ; paired 

 fins with well developed baseosts. Fin- 

 fulcra conspicuous, biserial. 



Scales thin, rhombic, deeply over- 

 lapj)ing, smooth or feebly ornamented; 

 principal flank scales dee])er than Ijroad, 

 ventral scales in part broader than deep; 

 a large scale at the base of one or both 

 lobes of the caudal, and three slightly 

 enlarged scales around the anus at base 

 of anal fin. 



Lateral line opening by widely sepa- 

 rated large pores. Paired fins without 

 baseosts. Fin-fulcra delicate. 



Scrutinizing the characters of Mr Darton's specimens in comparison 

 with the above table, the preponderance of evidence is seen to favor 

 their association with Pholidophori. Regarding the chief inharmonious 



Figure \.—Head of the so-called IsopJiolis {Ophiojisis) muensteri Wagner. 



Showing arrangement of facial bones characteristic of Eugnathidee : ar, articular; d, dentary; 

 ./((.r/, gular plate (displaced downward); pi, palatine; other letters as in figure 2. Specimen is 

 from lithographic slates (Upper Jura) of Kelheim, Bavaria (after Zittel). 



feature, arrangement of facial plates, the present material is inconclusive ; 

 more perfect forms may compel the erection of a new genus with liead 

 parts resembling Eugnathus, and partaking of the body characters of 

 Pholido'phorus. It will be coiivenient for the ])resent, however, to main- 

 tain the provisional reference to the latter genus. 



This species is not the only one to occupy an anomalous position for 

 kindred reasons. Certain S]iecies of Pholidophorus and Ojihiopsis are 

 united b}^ Zittel* under the new generic title of IsophoUs. The head 

 figured by him as /. muensteri^ a reproduction of which is given herewith 

 in figure 1, can not be distinguished from Eugnathus, but the vertebral 

 centra are stated to be well ossified, A, condition which is unknown among 

 Eugnathidae or Pholidophoridte. Agassiz's Pholidophorus longiserratus 



■Handbook of PalEeontology, vol. iii, 1S87, p. 21G, figure 230. 



