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III. — On the Structure of the Shoulder Girdle in Lystrosaurus. — 

 By E. Beoom, M.D., B.Sc, C.M.Z.S. 



In only a very few of the Anomodonts is the structure of the shoulder 

 girdle at present known. Owen described and figured (Cat. S. Af. 

 Eept., 1876) a portion of the scapula, the coracoid, and the imperfect 

 precoracoid of a small Dicynodont, and also a large Dicynodont 

 scapula. In 1880 (Q.J.G.S.) he figured the fairly good scapula and 

 sternum of " Platyjjodosaurus " (= Oudenodon). Seeley, in 1888 (Phil. 

 Trans.), described and figured the very imperfect remains of a small 

 Dicynodont reptile, which show the relations of the sternum cora- 

 coid and precoracoids to the interclavicle. Though Seeley makes 

 this specimen the type of a new genus (Keirognathus), there is 

 very little doubt that Lydekker (B. M. Cat. Foss. Kept., vol. 4, 1890) 

 is correct in regarding the remains as those of a small or young 

 Dicynodon. The scapula, coracoid, precoracoid, and sternum of 

 Oudenodon, have recently been described by myself (P. Z. S. 1901). 

 Hitherto, however, nothing has been known of the shoulder girdle 

 of Lystrosaurus {— PtychognatJms, Owen, — Ptychosiagum, Lyd.), 

 except an imperfect scapula of the Indian species — if, indeed, the 

 Indian species belongs to the genus. 



In the collection of the South African Museum is a small slab 

 showing a series of vertebrae with a sternum, the two clavicles, inter- 

 clavicle, portions of the right coracoid and precoracoid, and the 

 greater part of the right scapula of a species of Lystrosaurus. A 

 second specimen shows in good condition both scapulae and portions 

 of the left coracoid and precoracoid of a larger animal and possibly 

 a different species of Lystrosaurus. 



The sternum is large and flat and does not differ very greatly from 

 that in Oudenodon, though considerably larger proportionally. It is 

 moderately square, with the anterior and the two lateral angles 

 truncated. Its lateral and antero-lateral sides articulate with the 

 coracoids and precoracoids ; and the anterior end of the bone most 

 probably articulates with the interclavicle. 



The clavicles are well developed and only shghtly curved. They 

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