156 NEW YORK STATE MUSEUM 



same form, but are in the neighborhood of one fifth smaller than the corre- 

 sponding plates in the unique example of Mylostoma variabile 

 figured by Dean. It is necessary to bear in mind, however, in connection 

 with this author's restoration of the ventral armor, that the anterior and 

 posterior pairs of lateral plates have been confused with one another. 

 Such, at least, is the opinion of the present writer after comparison of the 

 plates marked by him ''Al'L" and '' PIV^" ^ with the ventrolaterals of 

 Dinichthys and noting specially their centers of ossification, growth-lines, 

 and nutritive canals. 



Formation and locality. Portage (Cashaqua) shale ; Mount Morris, 

 N. Y. There is also indistinct evidence either of this or of some species 

 of Mylostoma in the black Naples shale (Portage) at Sturgeon Point, on 

 the south shore of Lake Erie. 



GENERA OF DOUBTFUL FAMILY POSITION 



Fragmentary remains of Arthrodires, differing from other described 

 species as regards superficial ornament, and some of them indicating fishes 

 of considerable size, have been described from various Devonic localities 

 of the New York-Pennsylvania region. Most of the species are known 

 only by detached plates, none in association with the dentition, hence their 

 systematic position is doubtful. Coarsely tuberculated plates, suggestive 

 of Newberry's type of Aspidichthys c la vat us, are reported from 

 the New York Portage.^ As indicated by the generic name, the ornament 

 of Holonema consists of threadlike, radiating ridges. Two species are 

 known, the type ( H. rugosum Claypole) occurring in the Chemung of 

 New York and Pennsylvania, and the other (H. horridum Cope) thus 

 far known only from rocks of the same age in Bradford county, Pennsyl- 

 vania. One specimen of H. rugosum is interesting in that it displays 

 the entire ventral armor. Phyllolepis is distinguished from Holonema by 

 having the superficial rugae arranged in concentric, instead of radiating 



' Dean, B. Palaeontological Notes: On the Characters of Mylostoma Newberry. 

 N. Y. Acad. Sci. Mem. 1901. 2: 108, pi. 7. 



' AVilliams, H. S. U. S. Geol. Sur. Bui. 41. 1887. p. 43. 



