DEVONIAN FISHES OF IOWA 239 



terus taylori Hall,* founded on portions of a fish closely similar 

 to Holoptychius, is proved by the less complicated structure of 

 the teeth and obtusely lobate condition of the pectoral fins to 

 agree more closely with Rhizodonts, and is definitely assigned 

 to that family by Smith Woodward. 



The most commonly occurring scales of Holoptychius in the 

 Devonian of this country, and at the same .time the most widely 

 distributed, are those of H. giganteus Agassiz, and H. ameri- 

 canus Newberry. They are found not only in the Catskill of 

 the Appalachian region (the last-named form occurs in the 

 Chemung as well), but also in the Upper Devonian of south- 

 western Colorado. The scales of H. giganteus are very large, 

 those of the abdominal region externally ornamented with 

 closely set, thick, irregularly tortuous longitudinal ridges, often 

 branching and interrupted, more or less broken up into rounded 

 tubercles posteriorly. In H. americanus the ridges are sub- 

 parallel, strong, flexuous and sometimes inosculating, but not 

 disintegrating into tubercles nor interrupted to any appreciable 

 extent. H. lialli Newberry, from the Catskill of Delhi, New 

 York, is known by a unique example which displays a portion 

 of the trunk, and is covered with smaller and thinner scales than 

 those of the foregoing species. Other scales have been described 

 from the Catskill of Pennsylvania under the names of H. flabel- 

 latus, latus and serrulatus Cope ; and from the Chemung of the 

 same State are known H. filosus Cope, and H. granulatus, pus- 

 tulosus and tuberculatum Newberry. A single scale belonging 

 to an undetermined member of the genus is also reported by H. 

 S. Williams from the Chemung of Wellsville, New York.f Very 

 interesting from a distributional standpoint is the occurrence 

 of Holoptychian scales in the Upper Devonian rocks of East 



*Hall, J., Nat. Hist. New York, pt. iv. Geology, 1843, p. 282, text-fig. 130. 

 The type specimen is further noticed by Newberry in his Monograph of 1889, 

 p. 112, and portions of the skeleton are refigured by Dr. L. Hussakof in his "Cat- 

 alogue of the type and figured specimens of fossil vertebrates in the American 

 Museum of Natural History" (Bull. Amer. Mus. Nat. Hist. 1908, 25, p. 58, 59). 



tWilliams, H. S., On the fossil faunas of the Upper Devonian. Bull. U. S. 

 Geol. Surv. no. 4, 1887, p. 78. 



