74 



NEW YORK STATE MUSEUM 



Onchus rectus Eastman 



Text figure i6 



1899 Onchus rectus C. R. Eastman. N. Y. State Geol. 17th An. Rep't, p. 323, 



fig- 4 



Spines attaining a total length of about 5 cm, nearly rectilinear, 

 and gradually tapering to an acute point. Inserted portion round in 

 cross-section, very delicately striated ; exserted portion laterally com- 

 pressed, without trace of posterior denticles, the sides traversed by 

 about 10 fine longitudinal ridges. The latter are nonbifurcating, 

 regularly spaced, and of uniform size with the exception of the one 

 along the anterior margin ; this is twice the width of the others, and 

 is of triangular cross-section. 



Formation and locality. Chemung group ; Ontario and Western 



Railroad tunnel between Merrickville and North Walton, Delaware 



CO., N. Y. 



Genus homacanthus Agassiz 



This genus, which is evidently closely allied to Ctenacanthus, 

 is thus defined by Smith Woodward : '' Dorsal fin spines of small 

 size, slender, more or less arched, laterally compressed, and gradu- 

 ally tapering distally ; sides of exserted portion ornamented with 

 few, large, smooth, widely spaced longitudinal ridges ; a similar 

 ridge also forming a large anterior keel ; posterior face with a 

 double series of large, downwardly curved denticles." American 

 Pe"/!^^ species that have been referred to Homacanthus have, with but 

 Doririfin two exceptions, since been removed to other genera, but at least 

 at'size or*^ Devonic representative of this genus seems to be indicated by 

 the spines described in the following paragraph. 



■ 



Fig. 16 



sp: 

 Nat, 



