262 • IOWA GEOLOGICAL SURVEY 



1877. Palceoniscus cairnsii J. W. Dawson, Canadian Nat. n. s. 8, p. 339. 



1878. Palceoniscus cairnsii J . W. Dawson, Acadian Geology, Suppl., p. 100. 

 1891. Rhadinichthys cairnsi A. S. Woodward, Cat. Foss. Fishes Brit. Mus. pt. 



2, p. 465. 

 1904. Rhadinichthys cairnsi A. Tornquist, Zeitschr. deutsch. geol. Ges. 56, 

 p. 350. 



Trunk robust, with slender caudal pedicle, the maximum depth 

 somewhat greater than the length of the head with opercular 

 apparatus, and contained about four and one-half times in the 

 total length. Dorsal fin shorter than the anal, arising slightly 

 in advance of the latter. Scales of flank scarcely deeper than 

 broad ; scale-ornament consisting of delicate longitudinal striae, 

 parallel with the inferior border, and terminating in very fine 

 serrations of the posterior border (A. S. Woodward). 



From a comparison of Jackson's type specimens it is appar- 

 ent that the dorsal fin in this species is relatively somewhat 

 smaller and more remote than the corresponding structure in 

 R. alberti. 



Formation and locality. Same as preceding. 



Rhadinichthys modulus (Dawson). 

 (Text-fig. 39) 



1877. Palceoniscus modulus J. W. Dawson, Canadian Nat. n. s. 8, p. 337, 



woodcut fig. 1. 



1878. Palceoniscus (Rhadinichthys) modulus J. W. Dawson, Acadian Geology, 



3d Ed., Suppl., p. 100, woodcut fig. 18. 

 1891. Rhadinichthys modulus A. S. Woodward, Cat. Foss. Fishes Brit. Mus. 

 pt. 2, p. 466. 



A small species attaining a length of about 6 cm, in genera 1 

 resembling R. alberti, but described as distinguished by its rela- 

 tively shorter anal fin, the coarseness of the scale-ornament, 

 and ovate form of the dorsal ridge-scales. The ridge-scales be- 

 tween the occiput and dorsal fin are stated by Dawson to be ten 

 in number, of large size, oval in form, and sculptured with wavy 

 lines running subparallel with the lateral borders. The head is 

 elaborately ornamented with fine waving lines. 



The original description of this species is in reality composite, 

 being founded upon two individuals preserved in close proxim- 

 ity on the same slab of shale, one shown mostly in impression, 



