FISHES OF THE CARBONIFEROUS SYSTEM. 131 
strong and ingeniously devised joint. In Dinichthys a thimble-like process 
projects from the anterior border of the supra-scapula and plays in a conical 
cavity in the angle of the cranium. To prevent this conical condyle from 
getting wedged by sinking too deeply into the cavity, a guard projects 
from the under side of the angle of the head, upon which the supra-scapula 
rests. In Titanichthys the margin of the angle of the cranium is doubled, 
so as to form a deep groove, which is partially inclosed; that is, its margins 
approach each other. Into this groove a horizontal condyle, which is 
thinner behind than before, projecting from the anterior margin of the 
supra-scapula, may be slipped from the side. When thus inserted it cannot 
be directly withdrawn, but apparently had both a lateral and vertical 
motion. 
Aside from the parts just mentioned, the clavicles, corocoids (?), sub- 
orbital plates, the mandibles, and a ventral plate are all that have been dis- 
covered of the two known species of the genus. We are, therefore, without 
the means of making minute comparisons, part by part, with the much 
better known dermal skeleton of Dinichthys. We have data enough, how- 
ever, to determine that these gigantic bones represent a relative of Dinich- 
thys, and yet one widely different. The area of corresponding parts is 
greater in Titanichthys than in Dinichthys, but all the superficial bones are 
much lighter. A strong frame-work was, however, required for the locomo- 
tive apparatus of so large a fish, and some of the bones of the shoulder 
girdle are remarkably massive and strong. The corocoid (?), for example, 
is nearly two feet in length, and one end is a massive, subcylindrical bone 
nearly as large as one’s arm., The clavicles are more than two feet in 
length, but were composed of a relatively thin shell of bone, which was 
once lined and re-enforced with cartilage. The under jaws of Titanichthys 
are strikingly unlike those of Dinichthys. In one species, 7. Clarkui, they 
have the same general form; that is, the posterior end is a spatulate oar- 
blade, the anterior more massive, turned up like a sled-runner; while in 
T. Agassizii the entire mandible, though nearly three feet long, is a slender 
rod. The jaws are, however, alike in this, that instead of having cutting 
edges or rows of denticles along the upper margin the anterior portion is 
deeply furrowed, evidently to receive some kind of dental apparatus which 
