FOSSIL FISHES. 613 



flat plate, somewhat horizontally directed, but bent upward as it proceeds 

 forward; extremit}- truncated; the groove upon the upper surface of the 

 mandible forming a broad and shallow trough which becomes obsolete 

 anteriorly several inches before reaching the extremit) 7 ; the under sur- 

 face of the mandible slightly concave along its median axis, while the 

 outer and inner longitudinal angles are somewhat thickened and rounded, 

 the inner angle approaching the outer angle as it runs backward. 



To^al length of the portion figured 14 inches 



Breadth at anterior end If inches. 



Sreadth at posterior end 2£ inches. 



Greatest width of upper groove 2 inches. 



Locality; Cleveland Shale, east branch of Vermillion river, Florence, 

 Huron county, Ohio. Collected by Jay Terrell, Esq. 



The specimen upon which this species is based is one of a consider- 

 able series of Titanichthys bones in the museum of Oberlin College, dis- 

 covered by the indefatigable and experienced collector, Mr. Jay Terrell. 

 Although the posterior part of the mandible is missing, the most char- 

 acteristic anterior portion is perfectly preserved; and, as is well known, 

 no portions of the skeletons of the fossil fishes of the Cleveland Shale are 

 more distinctive than the mandibles. I have for comparison specimens 

 of the mandibles of T. Clarkii and T. Agassizii, of Newberry;* and 

 while the present species approaches the general outlines of T. Clarkii, 

 it is distinctly slighter and lacks the compressed form with narrow and 

 deep superior groove of that species, and has no approach to the tolera- 

 bly stout, gouge-like anterior extremity which characterizes T. Agassizii. 

 The exceedingly thin p ate. only an eighth to a sixteenth of an inch 

 thick and three or four inches long, into whjch the mandible is drawn 

 out anteriorly, seems to reach the climax of the surprising contrasts in 

 the skeletal structures of these tw T genera of huge fossil fishes Tita?iich- 

 thys and Dinichthys, which swam the seas of northern Ohio together in 

 the Paleozoic era. Especially is this true, as the weaker dentition belongs 

 to the larger fish. 



As to the nature of the functional surface of the mandibles of Ti an- 

 ichthys, whether it was covered with a horny sheath, or whether the 

 groove was set with bony "teeth," the specimens at my command yield 

 no positive information. The present species furnishes less suggestions 

 than does T. Clarkii that there was a horny sheath as Dr. Newberry 

 inclined to believe. None of the species of Titanichthys could have been 

 so predaceous as Dmichthys plainly was; and the present species would 

 seem to be a retrograde development from the more typical forms of the 

 genus, in that the possibility of any powerful use of the mandibles seems 

 to be more widely removed. This suggests that its food must have been 

 either simple vegetation or minute pelagic animals, which require no very 



* Paleozoic Fishes of N. Arn., Monographs U. S. Geol. Survey, vol. 16. 



