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Show 574 MR. R. LYDEKKER ON REMAINS [NOV. 19 to a process on the preaxial border, which he identifies with the acromial process of the Monotreme scapula, and marks by the letter e. This process is separated by a deep notch from the glenoidal region of the bone ; and above this process there is a long and deep emargination of the preaxial border (b of the figure), superiorly to which the distal extremity of the bone is expanded. Now from the absence of any other process between that marked e and the distal expansion of the bone, as well as from the general similarity in the position of the process in question, I am inclined to consider that its identification with the acromial process of the Monotreme scapula is in all probability correct. If this be so, the pectoral girdle of the Anomodonts will differ from that of the Monotremes in that the precoracoid-which I regard as the representative of the so-called epicoracoid of the latter-extended upwards to join the acromion. In plate lxix. figs. 5, 6, of his ' Catalogue,' Sir R. Owen figured a portion of the right side of a smaller pectoral girdle, which I have reason to believe belongs to the genus Ptychosiagum1 (Ptychognathus). Now in this specimen the scapula gives off a preaxial process for articulation with the precoracoid, which is clearly homologous with the one termed acromial in the preceding specimen, and is so lettered by Sir R. Owen. This acromial process differs, however, from that of Dicynodon in that it is separated only by a groove on the ventral aspect of the bone from the glenoidal region. Above this acromial process there is a shallow notch, on the dorsal side of which there occurs a projection which is shown by other specimens to be the distal extremity of the supraglenoidal portion of the preaxial border of the bone. The relations of these two processes are well shown in the right scapula of Ptychosiagum orientale represented in Plate LV. fig. 2, where it is quite clear that the upper or supra-acromial process b corresponds to b of Owen's figure. Tn redescribing the Owenian specimen in the 'Phil. Trans.' for 1888, p. 492, fig. 1, Professor Seeley correlates the process b with the acromion, not mentioning, however, what he would regard as the acromion in the scapula of Dicynodon, where, as we have seen, there is no process in the same position as b, or giving any reasons for his rejection of the determination of Sir R. Owen. Now it will be quite evident from the comparison of figs. 1 and 2 of Plate LV. that the processes marked a and b are homologous with one another, and consequently that a represents the one identified with the acromion in Dicynodon. In describing, however, the scapula of Platypodosaurus (Quart. Journ. Geol. Soc. vol. xxxvi. pi. xvii. fig. 1) Sir R. Owen wrongly identified the supra-acromial process (e of his figure) with the acromial of Dicynodon, regarding the true representative of the latter (/of his figure) as a portion of the glenoidal region ; whereas it will be evident from a comparison of Owen's figure with Plate LV. that his e corresponds with b and his / with a of the latter, which we have shown to be the acromial of Dicynodon. If, therefore, the process in the scapula of Dicynodon with which the precoracoid articulates is rightly identified with the acromial of 1 I bave proposed this name in place of Ptychognathus, wbicb is preoccupied. |