DEVONIAN FISHES OF IOWA 75 



the more thickened plates. The external ornament always con- 

 sists of tubercles and coarse rugae. At least one membranous 

 dorsal fin is present, and in Bothriolepis two have been detected 

 by Patten. The tail, either naked or scaly, is furnished in 

 Pterichthys at least with a large membranous caudal fin of gen- 

 uinely heterocercal form. 



The forms belonging to this order are included within a single 

 family, the Asterolepidae, sometimes, but incorrectly called the 

 ' ' Pterichthyidae ". The typical genus, Pterichthys (text-figs. 

 8-11), is not known to occur in this country; but the Upper De- 

 vonian Bothriolepis, which differs from Pterichthys principally 

 in its longer appendages, scaleless tail, and minor details of the 

 body armor, is found both in the eastern part of North America 

 and in Colorado, four species having been described from this 

 continent in all. Asterolepis itself appears to be represented by 

 portions of the body armor occurring in the Chapman sandstone 

 of Aroostook county, Maine, the accompanying invertebrates in- 

 dicating a lowermost Devonian horizon. This species, which 

 has been described under the name of A. clarkei, is noteworthy 



,FlG. 8. 



Fig. 8. Pterichthys testudinaris Agassiz. Lower Old Red Sandstone; Scotland. Left 

 lateral aspect, restored by Dr. R. H. Traquair, x J. 



for continuing the history of Asterolepids back to a more remote 

 period than has previously been known for this group. The so- 

 called Astraspis desiderata of Walcott, from the Ordovician 

 (Trenton) of Canyon City, Colorado, by some conjecturally re- 

 ferred to the Asterolepidae, is of entirely problematical nature. 



Family ASTEROLEPIDAE. 



Head and body covered with dermal plates which are exter- 

 nally sculptured and tuberculate, the dorsal and ventral shields 

 of the trunk firmly united by the lateral plates. Orbits very 

 closely approximate, separated by a loose interorbital median 



