D. M. S. Watso7i — Liinhs of Lystrosaurus. 257 



ectepicondylar perforation. The bones of the forearm agree with 

 those of the Albany Museum skeleton. The radius is a short bone, 

 with a narrow, nearly circular, shaft, expanded at the top to a head, 

 which is provided with an articular face divided by a ridge into two 

 parts, the anterior articulating with a face on the front of the humerus, 

 the other jointing with that on the head of the ulna to articulate 

 with the end of that bone. The lower end is much expanded laterally. 

 The ulna has a stout head of triangular section, its antero-internal 

 face articulates with the head of the radius, and its articular face for 

 the humerus is continuous with one of those of the other bone. There 

 is no produced olecranon process, but the bone lias obviously had 

 a cartilaginous expansion in this region. The shaft is thin and the 

 lower end laterally widened. 



As in all Anoinodonts, the forearm was carried at right angles to 

 the humerus and had probably only a very limited range of movement. 

 Looked at from the front, the head of the radius lies before a good 

 deal of the head of the ulna, so that there is some crossing. iStudy 

 of well-preserved shoulder-girdles shows that the humerus was carried 

 generally at right angles to the body, as in most primitive reptiles and 

 the living Monotremes. In this individual there is no ossification in 

 the carpus, and its length is uncertain. All five metacarpals are 

 preserved ; the first is a rounded nodule of bone, from the second to 



Fig. 2. The upper ends of the radius and ulna of the specimen represented 

 in Fig. 1. X i. 



the fifth there is a perceptible shaft, and the bones increase in length 

 to the fourth, which, as is usual in reptiles, is the longest. 



The first phalange of each digit is a curious nodule of bone, which 

 in longitudinal section is triangular, the dorsal surface being flat and 

 the two articular surfaces nearly meeting below. The second 

 phalange of the first digit is not preserved ; those of the other 

 fingers are flat, and have a trace of a shaft in a notch on either edge. 

 Their articular faces are parallel. The third phalanges of the third, 

 fourth, and fifth digits are flat, very thin, and spreading. Taken 

 as a whole the hand is an aquatic modification of the ordinary 

 Anomodont type ; the chief modifications are the excessive breadth, 

 the flattening of all the bones, and the great expansion of the 

 terminal phalanges. The most cuj-ious feature is the triangular 

 section of the first phalange, which allows of very great flexion of the 

 digits ; the same feature occurs in Kannemeyeria and in Monotremes, 

 to the foot of which that of Anomodonts offers many striking 

 resemblances, as Owen, Seeley, and Broom have already recognized. 



Amongst the series of South African fossils presented to the 

 British Museum by Mr. David Draper, the well-known Johannesburg 

 geologist, is an extremely well-preserved fragment of Lystrosaurus 



DECADE V. — VOL. X. — NO. VI. 17 



