DEVONIAN FISHES OF IOWA 83 



genus has until recently been supposed to be confined to the 

 Upper Devonian, but indications of a proemial species, which 

 has received the name of A. clarkei in honor of the New York 

 State Geologist, are now known to occur in the lowermost De- 

 vonian (Chapman sandstone) of Aroostook county, Maine. In 

 the opinion of Dr. J. M. Clarke, the accompanying invertebrate 

 forms indicate an assemblage having a strong element of af- 

 filiation with the Coblenzian (Lower Devonian) of the Rhine 

 district, and certain identities with the Helderberg and Oris- 

 kany of New York State. 



Genus bothriolepis Eichwald. 



Premedian plate of headshield not notched in front; post- 

 median small, not excluding the median occipital from the pos- 

 terior border of the orbit; extralateral, if present, small and 

 narrow. Posterior commissural canal of headshield formed by 

 a V-shaped groove, the apex of which is situated on the median 

 occipital, and the anterior termini in about the center of the 

 lateral plates. Anterior dorsomedian plate overlapping the 

 antero-dorsolateral, but overlapped by the postero-dorsolateral 

 plate. Pectoral appendages at least as long as the armored 

 trunk, segmented into a distal and proximal portion, the latter 

 being much larger than the former, which is narrow and taper- 

 ing; marginal scutes of the proximal portion meeting mesially, 

 with a minute anconeal element only on the dorsal aspect ; articu- 

 lar plates in contact for some distance above the external mar- 

 ginal on the outer aspect; marginal and central scutes of the 

 distal portion more numerous than in Pterichthys. Tail naked ; 

 two dorsal fins. 



A knowledge of the structure of this genus being indispensable- 

 for a correct understanding of the group, it is not surprising that 

 the exquisitely preserved specimens of B. canadensis, from the 

 Upper Devonian of Quebec, should have invited the most search- 

 ing investigation on the part of palseiehthyologists. The Cana- 

 dian material is certainly unrivaled for exhibiting finer anatom- 

 ical details, and but for the information so derived it would oe 

 difficult to interpret the poorly preserved remains occurring else- 

 where in North America and in Europe. Bothriolepis is re- 



