204 



IOWA GEOLOGICAL SURVEY 



the oral margin as if for a horny sheath, and somewhat turned 

 upwards at the symphysis. Outer (free) portion of clavicular 

 developed as a stout arm, rounded or semicylindrical in cross- 

 section. 



The remarkable fishes comprised by this genus represent the 

 ultimate stage of specialization attained by Dinichthyids. Un- 

 able to maintain an existence except under peculiarly favorable 

 conditions — their gigantic size, unwieldy organization and weak 

 dentition presupposing an estuarine habitat and abundant food 

 supply — they survived for a relatively short period, and within 

 a limited area. Their remains are confined, so far as known, to 

 the Upper Devonian of Ohio. Forerunners of the genus, how- 

 ever, make their appearance as early as the Ulsterian, and frag- 

 mentary plates very suggestive of Titanichthys occur in the 

 Hamilton limestone of Milwaukee, Wisconsin. 



Fig. 81. 



Fig. 31. Titanichthys apassizi Newberry. Restoration of headshield and dorsal armor- 

 ing of trunk. ADL, antero-dorso-lateral, fused in the type specimen with the postero- 

 dorso-lateral; C, central; DM, dorso-median restored after the outline of T. clarki: EO, ex- 

 ternal occipital; M, marginal; MO, median occipital; P, pineal; if, position of rostral; SO, 

 suborbital, x 1-16. 



Compare figures of body plates given in Hussakof's "Catalogue of Fossil Fishes", 

 (Bull. Amer. Mus. Nat. Hist. 1908. 35, p. 20). 



