EXPLANATION OF PLATE XXIII. 
The upper figure represents the left side of the skull which bears Professor Marsh’s number 
1922 (U. 8. N. M., No. 2673). The mandible on the right side is dislocated and crushed down. 
The lower figure represents the right side of the skull which bears Professor Marsh’s number 
1921 (U.S. N. M., No. 2672). The specimen is badly broken and crushed in part, but the occip- 
ital region is in part better preserved than is the case in the specimen represented in the upper 
figure. The drawings of the skull of Diplodocus published by Professor Marsh, as well as other 
drawings, which he caused to be made, but which he did not publish for reasons which are plain 
to the critical student, show that he utilized both of these skulls in preparing his descriptions and 
published figures. 
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