DEVONIAN FISHES OF IOWA 241 



longing to the Museum of Comparative Zoology at Cambridge 

 is figured for comparison in the same plate (fig. 12). 



By far the most abundant of any species of this genus is that 

 which Newberry described under the name of 0. hopkinsi, oc- 

 curring typically in the Chemung of Delaware county, New 

 York, but being also represented in enormous quantities in the 

 basal bituminous layer of the Marcellus shale in the same State. 

 The average length is stated by Newberry to be about 2.5 cm. 

 This, together with the considerable stratigraphic interval sep- 

 arating the smaller teeth from 0. sigmoides , probably furnishes 

 sufficient reason for maintaining them as distinct species. A 

 series of five well preserved presymphysial teeth belonging to 

 0. hopkinsi, from the Chemung of Franklin, New York, is shown 

 in Plate I, fig. 3. 



An undetermined species of Onychodus seems to be indi- 

 cated by a few detached plates, teeth and jaw-fragments from 

 the Cedar Valley limestone of Bremer county, Iowa, and the 

 Hamilton of Oran, Onondaga county, New York. A single de- 

 tached scale from the latter locality, closely resembling those 

 of the type species, is shown in Plate I, fig. 11. Supposed Cross- 

 opterygian scales with longitudinally striate ornamentation 

 occur also in the Portage beds of Livingston county, New York. 

 It is possible that some of these may be of Coelacanthid nature, 

 but until other parts of the skeleton are known, their precise 

 determination is impossible. 



Suborder ACTINISTIA. 



The extremely specialized Crossopterygians embraced by this 

 suborder have frequently been cited as furnishing perhaps the 

 most remarkable example of a persistent type that we are ac- 

 quainted with among fishes, continuing as they do practically 

 unchanged from the Upper Devonian to the close of the Creta- 

 ceous. As noted by Smith Woodward, the group has become 

 specialized chiefly by degeneration, one of its characteristic 

 features being "the large symmetrical caudal fin, which ex- 

 hibits a series of supports directly apposed to the neural and 

 haemal arches, equalling in number both these and the over- 

 lapping dermal rays." 



16 



