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CROSSOPTEKYGII. 



each supporting a ' laniary ' tooth ; a pair of similar teeth on the 

 roof of the mouth, but the marginal upper dentition feeble. Teeth 

 conical, with a very small pulp -cavity, of which the walls exhibit 



Pig. 48. 



Transverse section of Holoptychian (Dendrodont) Tooth, much magnified ; 

 after Pander. 



complex infoldings, appearing closely intertwined when viewed in 

 transverse section, these producing superficial vertical flutings. 

 Pectoral fins acutely lobate, pelvic fins acutely or obtusely lobate ; 

 two remote dorsal fins ; anal fin single ; caudal fin diphycercal or 

 heterocercal. 



The typical Holoptychius is the single genus of this family as yet 

 definitely determined. 



Genus HOLOPTYCHIUS, Agassiz. 



[Agassiz in Murchison's Silur. Syst. 1839, p. 599 (Holoptychus), 

 and Poiss. Foss. V. G. E. 1844, p. 68.] 



Syn. Dendrodus, E. Owen, Microscopic Journal, vol. i. 1841, p. 4. 



Platyynathus, L. Agassiz, Poiss. Foss. V. G. E. 1844, pp. 61, 76. 



Lamnodus, L. Agassiz, ibid. 1845, p. 83. 



(?) Sclerolepis, E. von Eichwald, Bull. Soc. Imp. Nat. Moscou, 



vol. xvii. 1844, p. 828. 

 (?) Apedodus, J. Leidy, Journ. Acad. Nat. Sci. Philad. [2] vol. iii. 



1856, p. 164. 

 (As subgenus) Glyptolepis, L. Agassiz, Poiss. Foss. V. G.E. 1844, 



p. 62 (in part). 



Body short and stout, not much laterally compressed ; scales large 

 and rounded, the exposed surface marked with large, longitudina 



