42 ANNUAL REPORT OF 



Fig. 4. 



Coccosteus decipiens Ag. Lower Old Red Sandstone; Scotland. Lateral 

 aspect, restored by Dr. R. H. Traquair. X J A- 



hugest of all Palaeozoic fishes, Dinichthys and Titanichthys, 

 which occur in the uppermost Devonian of Ohio and neighboring 

 States. The length of these creatures has been estimated at 

 upwards of fifteen or twenty feet, and the solidity of their armor- 

 plating has never been surpassed amongst fishes. Over the back 

 and head the bones were in places fully three inches thick, and 

 exceedingly dense, though in smaller forms, of course, the arm- 

 oring was lighter. Equally effective was their dental armature, 

 Dinichthys having in the upper jaw a pair of beak-like incisors, 

 behind which were formidable shear-teeth; and in the lower jaw 

 a large and exceedingly powerful dental plate, likewise provided 

 with a beak-like projection in front. It is evident that these 

 creatures could not have been very mobile, owing to their cum- 

 bersome armor and lateral expanse of body, Titanichthys having 

 a total width of about six feet; and it is further obvious from 

 the character of sediments that they frequented the mouths of 

 shallow estuaries, where they maintained probably a not very 

 active existence. The characters already enumerated, such as the 

 peculiar dermal plating, cartilaginous axis, and non-articulation 

 of the lower jaw with the cranium, separate Arthrodires widely 

 from modern bony fishes. 



Considerable numbers of these armored creatures nourished 

 throughout the Devonian, but became extinct at the close of that 

 period without leaving any descendants. It is worth while to 

 take note, in passing, of these and similar instances of extinction, 

 which have in times past affected not only species and genera, 

 but entire groups of organisms, sometimes without any discernible 

 cause! N0 1 doubt in the majority of cases large groups become 

 crowded out through the incessant and relentless struggle for 



