40 NEW YORK STATE MUSEUM 



external marginal. Postmedian plate of the head large and broad, exclud- 

 ing the median occipital from the margin of the orbit ; premedian plate 

 notched in front ; extralateral plate loosely articulated with the rest of the 

 cranial shield. Superficial ornament consisting of raised tubercles with 

 stellate bases, which may be sometimes confluent. Lateral line system on 

 the head connected by two commissural canals, a posterior one crossing 

 the hinder part of the median occipital, and an anterior one crossing the 

 premedian plate in front of the orbit. Tail unknown. 



The characters of this genus, so far as known, do not differ from those 

 of Pterichthys except as regards the mode of articulation of the anterior 

 median dorsal plate, and in the arrangement of the terminal plates of the 

 pectoral appendage. No specimens of Asterolepis have yet been discovered 

 however which show the tail. Like Bothriolepis this genus has hitherto 

 been supposed to be confined to the Upper Devonic, but the species imme- 

 diately to be described proves that its geological antiquity is almost equal 



to that of Pterichthys.' 



Asterolepis clarkei sp. nov. 



Plate 7, figure 7, 8 



An imperfectly definable species, known only by a unique example of 

 the posterior dorsomedian plate, which is about two thirds the size of that 

 in A. maxima, and exhibits the characteristic features of the genus. 

 The plate is steeply arched from side to side, the slopes uniting mesially 

 in a longitudinal carina along which the tubercles are densely crowded, and 

 in part overlapping. Elsewhere the surface is covered with relatively 

 coarse, conical nonstellate tubercles, which are rarely confluent, but tend 

 to become arranged in concentric fashion over the anterior portion of the 



'That is to say, on the assumption that the obscure fragments from the Siluric of the 

 Baltic provinces described by Pander as P. elegans, P. harder i, and P. striatus 

 properly belong to this genus. The species which have received these names are regarded 

 as possibly founded upon fragments of Asterolepis ornata by E. von Eichwald, 

 Lethaea Jiossica, i860, i: 1507. Portions of Asterolepidlike appendages have also been 

 described by Professor Patten from the Siluric of Oesel, but are referred by him with 

 very slight probability to Treniataspis amongst the Osteostraci, in which such organs are 

 unknown. ["On the Appendages of Tremataspis." Am. Nat. 1903. 37: 223-42.] 



