104 IOWA GEOLOGICAL SURVEY 



part branching; these exhibit more numerous segments than 

 those of the other median fins. Complete skeletons of Pleur- 

 acanthus have been found only in the Coal Measures of Com- 

 mentry, France, in the Lower Permian Coal Measures of Ger- 

 many and Bohemia, and in the Lower Hawkesbury Formation 

 of New South Wales; but detached spines and teeth indistin- 

 guishable from those of this genus occur also in the [Devonian, 

 Mississippian and] Coal Measures of North America and in the 

 lowermost Carboniferous strata of Scotland, while a few teeth 

 have been found even in the Upper Trias (Keuper) of Somer- 

 setshire. 



Genus diplodus Agassiz. 



Under this name are comprised a number of Palaeozoic species 

 founded only upon the evidence of detached teeth, hence the 

 status of the genus is more or less provisional. This fact being- 

 understood, it is convenient to retain the generic title pending 

 such time, as our knowledge of the entire organization becomes 

 more complete, notwithstanding the prior employment of Dip- 

 lodus among modern bony fishes (porgies, bass). Mr. S. A. 

 Miller, in his work on North American Geology and Palaeon- 

 tology, has proposed its replacement among fossils by Dissodus ; 

 and Dr. 0. P. Hay prefers the substitution of the earlier syn- 

 onym of Dittodus. 



Diplodus pricus Eastman. 



(Plate I, Figs. 5, 13) 



1899. Diplodus imscus C. R. Eastman Journ. Geol. 7, p. 490, pi. 7, figs. 1, 2. 

 1899. Diplodus priscus S. Weller, Journ. Geol. 7, p. 484. 

 [' 1907. Diplodus priscus C. R. Eastman, Mem. N. Y. State Mus. 10, p. 59, pi. 

 1, figs. 7, 8. 



Teeth minute ; the two principal cusps of dental crown diverg- 

 ent and slightly inclined backwards, robust, conical, circular in 

 section, without lateral carinae; coronal surface marked with 

 relatively few prominent, slightly curved striae extending from 

 the base nearly to the extremities on the anterior face, but short- 

 er and usually fainter on the posterior face. Median denticle slen- 

 der, sometimes much reduced, or in one specimen wanting alto- 

 gether. Anterior border of root slightly produced downward; 

 lower surface concave, elliptical in outline; posterior button 

 present. 



