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Show 168 MR. G. A. BOULENGER ON [Feb. 17, British, having been found along with other unnamed fossils from country in the Museum of the College of Surgeons. I have submitted the specimen to m y colleague Mr. Etheridge, who was so kind as to examine the matrix and have a section of it prepared, and he informs me that the fossil is in all probability from the Forest Marble, Bath Oolite, of Chippenham or Corsham, Wiltshire. Mr. A. Smith Woodward, for whose kind advice I likewise applied, on being shown the specimen at once produced another, a left maxillary showing its inner aspect, of what I believe to be probably the same animal, but surrounded by a very different matrix. This specimen, recently acquired for the British Museum from Mr. P. Rufford, was obtained in the Purbeck beds of Swanage, Dorsetshire ; it bears the Museum Register No. R. 1765, had been identified by Mr. Woodward as Rhynchocephalian, and was most courteously placed by him at my disposal for examination. The left ramus in the Museum of the College of Surgeons is imperfect anteriorly, but the missing portion cannot have been great, as may be deduced from the condition of the teeth, of which there are seven, gradually decreasing in height from back to front, so that the symphysial end of the mandible must have had a sharp, nearly straight edge, as we know to be the case in Homceosaurus. The coronoid process is perfectly preserved, triangular, its height nearly equalling that of the jaw. The postcoronoid portion is lost, but has left its impression on the stone, and it agrees with the corresponding part in Homceosaurus, differing in its shortness from Sphenodon. The bone is of a dark brown colour. The length of the entire mandibular ramus must have been about .'^5 millim., as against 25 in H. maximiliani. In this respect it agrees with the specimen from the Kimmeridgian of Hanover described by Struckmann1. There is no doubt, in my opinion, that the larger size of the Hanover specimen is not to be attributed to age, considering the state of the dentition in the typical H. maximiliani, which indicates an adult animal ; and as I can find no difference between the Hanover specimen and the mandible described above, I propose to designate them both as H. major. Comparison cannot, unfortunately, be instituted with Sapheosaurus, H. v. Mey., which agrees very uearlv in size, but of which the mandible and the alveolar border of the maxillary are still unknown. As regards the systematic position of Homceosaurus, there can be no doubt that it stands in close relation to the living Sphenodon, from which it differs, however, in three important points, viz. the absence of the ectepicondylar foramen in the humerus, the absence of uncinate processes to the ribs, and the absence of intercentra or hypapophyses between the dorsal vertebrae, to which characters a fourth may probably be added, viz. the fuller ossification of the vertebral centra, which appear to be less deeply excavated at either end than in Sphenodon. All these characters, except the absence of uncinate processes, may be regarded as indicating a higher development in the Rhynchocephalian line. I hold that of the two most recent writers on the ' Zeitschr. deutsch. geol. Ges. xxv. p. 249, pi. vii. (1873). |