324 DR RAMSAY H. TKAQUA1R ON FOSSIL FISH-REMAINS 



Incertse Sedis. 



Order ARTHRODIRA. 



Family (?) Coccosteid^. 



Genus Holonema, Newberry. 



Generic Characters. — Imperfectly known. The genus was instituted for thin, 

 rather large plates covered externally by closely set ridges or rugse radiating from a 

 central point towards the circumference, but often, too, especially in the middle of a 

 plate, irregular or reticulated. The plates as yet known seem to belong to a ventral 

 cuirass of Coccostean structure. 



History. — In 1883 the late Professor Claypole described and figured what he 

 designated as a " large fish plate from the Upper Chemung (?) beds of North 

 Pennsylvania."* This plate he considered to be probably the median ventral plate of 

 a species of Pterichthys — the "lozenge" plate of Hugh Miller. 



The plate itself is of an oblong pentagonal form, having one very short side placed 

 transversely at the supposed posterior extremity, followed by two pairs of laterally 

 symmetrical sides, of which the shorter pair meet at an angle on the supposed anterior 

 aspect. All round is " a flat, finely striated margin " — namely, the narrow area over- 

 lapped by adjoining plates — within which the exposed surface is sculptured with 

 radiating, closely set, subparallel rugse, more or less perpendicular to the margin, though 

 in the centre of the plate tending to show an irregular reticulation. 



This plate, evidently a median one, Claypole considered to belong to a new species 

 of Pterichthys, and to represent the median ventral or " lozenge " plate of Hugh Miller. 

 Accordingly he named it Pterichthys (?) rugosus, noting, however, that Professor 

 Newberry, to whom he had sent a photograph and description of the specimen, had 

 informed him in a letter that he (Professor Newberry) " very much doubted if the 

 plate here described belonged strictly to Pterichthys, and was inclined to consider it 

 the type of a new genus." 



Six years afterwards Newberry, in his special work on the Palseozoic Fishes of 

 North America,^ figured some further plates of the same fish from the "Chemung" 

 strata, which he felt necessary to separate generically from Pterichthys, though retain- 

 ing Claypole's name for the species, which he now designated Holonema rugosum. 

 In PI. XVII. of the work he reproduces Claypole's figure (fig. 2) and adds representa- 

 tions of three other pieces. In fig. 1 we have a rather large fragment, in which the 

 rugse, frequently bifurcating, radiate from nearly a central point, while in fig. 4, 

 obviously a fragment, the point of radiation is at one side ; lastly, in the remaining 

 fragment, shown in fig. 3, the ruga3 are in some places contorted and irregular. It is 

 to be noted that, although Newberry nowhere directly states his opinion as to the 



* Proc. American Phil. Soc, vol. xx. (1883), pp. 664-666, with figure. 



t Palaeozoic Fishes of North America (Washington, 1889), pp. 92-95, pi. xvii. figs. 1-4. 



