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464 OSBORN, THE REPTILIAN SUBCLASSES DIAPSIDA AND SYNAPSIDA. Testudinata) are singularly constant in the exhibition of the formula 2, 3, 3, 3, 3, which is very little removed from that of the Stegocephala, and is identical with that of mammals. In certain aquatic Testudinata (Trionychoidea) the formula secondarily rises nearly to that of the Diapsida. In the earliest Plesiosauria the S f cor. f.cor. Fig. 7. Synapsidan and mammalian types of shoulder girdle. A-D, after Seeley; E-F, after Howes. A, Pareiasaurus bainii. B, Keirogatkhus cordylus. C, Deuterosaurus. D, Rhopalodon. E, ventral; E', lateral views of Ornithorhynchus. F, Leous. formula of the manus is not definitely known; it is recorded as 2, 3, 4, 4, 3 (Lariosaurus, Boulenger) but may be higher; the formula of the pes, as recorded, is truly Diapsidan, namely 2, 3, 4, 5, 4 in Lariosaurus. We must therefore await the discovery of the ancestors of the Sauropterygia before this group can be positively considered of Synapsidan origin in respect to this character. C t- DQ
OSBORN, THE REPTILIAN SUBCLASSES DIAPSIDA AND SYNAPSIDA. 465 Epfifhyses. A fact which may prove to be of some importance is the reported presence of the characteristically Mammalian elements, rudimentary epiphyses, in certain Plesiosauria (Kukenthal) and Testudinata (v. Zittel). V.-SUBCLASS SYNAPSIDA. Next to the Cotylosauria, which have already been characterized, the Anomodontia are to be regarded as the stem forms of Synapsida. They apparently bear the same general ancestral relation to the Chelonia, Plesiosauria, and Mammalia that the Diaptosauria bear to the higher Diapsida. These remarkable Permian and Lower Triassic reptiles should be clearly separated from the Cotylosauria or Pareiasauria, with which they are by some authors confused. The Anomodont forms known at present, through the researches of Owen, Seeley, and Broom, exhibit an adaptive radiation of terrestrial, ambulatory, carnivorous, herbivorous, and possibly aquatic (Placodontia) forms analogous to that of the Creodont Mammalia. When we discover the, as yet unknown, smaller, short-limbed, littoral and amphibious members of the Anomodontia we shall probably be not far from the ancestry of the Sauropterygia and Testudinata, which is at present uinknown. Similarly, in my opinion as expressed several years ago,' the discovery of small unspecialized insectivorous Anomodonts will bring us near the ancestry of the Mammalia. In other words, the adaptive radiation of the Anomodonts will furnish us with the ancestry of all the Synapsidan orders. The Coracoid and Procoracoid in Sauropterygza and Che/onia.-In this connection the question of the homologies of the bones composing the shoulder girdle of the Plesiosaurs and Testudinata becomes of very great importance. There has been a strong tendency recently to compare and homologize these elements very closely; btut there is danger of mistaking analogies for homologies. We have as yet received no final palaeontological demonstration of the bone representing the procoracoid in the earliest Plesiosaurs. It may be said that such high authorities as Gegenbaur and his successor, Fiurbringer, both regard the anterior ventral process of the scapula in the Testudinata as a modified procoracoid. On the other hand, Baur, Howes, and other equally reliable authorities regard this process as a development from the scapula, in other words, as a proscapular process. If the latter view be correct we must await further knowledge of the Lower Triassic Testudinata to show the fate of the procoracoid element in the Chelonia. Whatever the homology of the anterior ventral element of the shoulder girdle of these orders proves to be, a separation of the procoracoidfrom the coracoid is an unquestionable characteristic. The known Permian and Lower 1 The Origin of the Mammalia. Amer. Nat., Vol. XXXII, May, I898, p. 333. Also Amer. Journ. Sci., Vol. VII, Feb., I899, p. 95.
Page 1 and 2: MEMOI RS OF THE Se t r H isto-ry. V
Page 3: VOLUME I, PART VIII. THE REPTILIAN
Page 6 and 7: 452 OSBORN, THE REPTILIAN SUBCLASSE
Page 34 and 35: Po.Qi 480 OSBORN, THE REPTILIAN SUB
Page 36: 482 OSBORN, THE REPTILIAN SUBCLASSE
Page 40 and 41: Fig. 17 a. Stereosternum tumidum Co
Page 42 and 43: | J j 486 OSBORN, THE REPTILIAN SUB
Page 62 and 63: ol 506 OSBORN, THE REPTILIAN SUBCLA
Page 65 and 66: INDEX TO VOLUME I. [New names of ge
Page 67 and 68: Aphelops profectus, 358, 373 superc
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Hoplophoneus pr1mevus, 394 robustus
Page 71 and 72:
Pleurosaurus, 463, 468, 494, 495, 4
Page 73 and 74:
Sesia albicornis, 226, 229, 230, 27
Page 75:
Trochilium tipuliformis, 286 tricin
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