1 68 NEW YORK STATE MUSEUM 



are very large, those of the abdominal region externally ornamented with 

 close, thick, irregularly tortuous, longitudinal ridges, often branching and 

 interrupted, more or less replaced posteriorly by rounded tubercles. In 

 H. americanus the ridges are subparallel, strong, Hexuous and some- 

 times inosculating, but not broken up into tubercles or interrupted to any 

 appreciable extent. H. halli Newberry, from the Catskill of Delhi, N. Y., 

 is known by a unique example which displays a j:)ortion of the trunk, and is 

 covered with smaller and thinner scales than those of H. americanus. 

 The type of this species is preserved in the New York State Museum at 

 Albany. Other species described from the Catskill of Penns)'lvania are 

 H. flabellatus, H. latus and H. serrulatus Cope; and from the 

 Chemung of the same state are known H. f'losus Cope, H. granu- 

 latus, H. p u s t u 1 o s u s and H. tubercu latus Newberry. A single 

 scale belonging to an undetermined species of Holoptychius is also reported 

 by H. S. Williams from the Chemung of Wellsville, Allegany co., N. Y." 

 Family onychodonxida.ec 



Scales cycloidal, deeply overlapping. Head and opercular apparatus 

 with well developed membrane bones. Dentary bone of mandible thin and 

 deep, bearing a single close series of large conical teeth, flanked by an 

 outer series of very minute teeth ; an azygous series of large more or less 

 recurved teeth attached in front of the sj'mphysis. Teeth plicated onl)- at 

 the base, with a central cavit)' ; dentary teeth tipped only, presymphysial 

 teeth completely enveloped with enamel. 



But a solitary genus, Onychodus, is at present known to represent this 

 family, and its remains have hitherto been found only in a fragmentary con- 

 dition. Such bones of the cranial roof and jjectoral girdle as are known 

 suggest a certain resemblance to the Holoptychiidae and Rhizodontidae. 

 The tooth structure, however, is simple, and a ccMispicuous difference exists 

 in the presence of a dentigerous presymphysial bone. The external bones 

 and scales of the type species, O. sigmoides Newberry, are ornamented 



• AVilliams, H. S. On the Fossil Faunas of the Upper Devonic. U. S. Geol. Sur. Bui. 

 4. 1887. p. 78. 



