1992.] 223 [Cope. 



from end to end of the plate. The anterior part of the external border 

 of tlie plate is present in the rock mold, so that a cast of its surface was 

 not obtained ; but, with this exception, the cast is nearly complete. On 

 the middle of the plate, commencing at the anterior extremity, ihe ridges 

 are least interrupted. Anteriorly they are oblique or slightly imbricate, 

 looking outwards, and are connected at longer intervals ; near the inner 

 border, but little connected. Posteriorly they are more direct and are 

 more frequently joined by transverse connecting ridges. Near the mid- 

 dle of the external region the ridges so inosculate as to produce a non- 

 linear arrangement of round pits. On the inner side of the plate the 

 sculpture Is finer and is longitudinally honeycombed. 



MM. 



Total length of plate 120 



Width at middle 60 



Length of anterior internal border 90 



Length of posterior internal border . . 47 



In the roughness of its surface this species exceeds those that are 

 known to belong to the Antiarcha. 

 Chemung bed, Bradford county, Pa., A. T. Lilley. 



HoLONEMA RUGOSA Clayp. 



Newberry Paleozoic Fishes of N. Amer., 1889, p. 92. 

 Pterichthys rugosus Claypole, Proceeds. Amer. Philosophical Soc, 1883, 

 p. 664. 



Fragments of the exoskeleton of this species are common in the Che- 

 mung beds, and they are generally of large size, much exceeding that of 

 any other species of the Bothriolepididte. They are generally so much 

 broken as to render their location difficult. I obtained from Mr. Lilley a 

 number of fragments of such a plate, which, on reconstruction, proves to 

 belong to the posterior median dorsal plate, enough of which remains to 

 give a good idea of its form and sculpture. The anterior margin only is 

 entirely wanting. 



The plate is obtusely rounded at the median line, giving an obtusely 

 roof-shaped form. It Is relatively rather narrow anteriorly, and widens 

 gradually to the posterior border, where it is also flatter. The edges (lat- 

 eral and posterior) are rather thin, and the lateral are obscurely beveled 

 below, as though to overlap the lateral posterior plates. The middle line 

 below is openly grooved on the anterior half, while a longitudinal thick- 

 ening marks the middle line of the posterior fourth below. Tlie inferior 

 surface is smooth, while the superior surface is sculptured with the par- 

 allel grooves characteristic of the species. These grooves extend to the 

 lateral and posterior borders. The median ones are longitudinal and 

 without interruption throughout the length of the fragment. Those on 

 each side of the middle line diverge slightly and reach the margin, the 

 lateral at an acute angle as far forward as the middle of the length of the 



PROC. AMER. PHILOS, SOC, XXX. 138. 2 C. PRINTED MAY 24, 1892. 



