168 MR. G. A. BOULENGER ON [Feb. 17, 



British, having been found along with other unnamed fossils from this 

 country in the Museum of the College of Surgeons. I have submitted 

 the specimen to my 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 corre- 

 sponding part in Homceosaurus, differing in its shortness from Sphe- 

 nodon. The bone is of a dark brown colour. The length of the 

 entire mandibular ramus must have been about 35 millim., as against 

 2.5 in H. maximiliani. In this respect it agrees with the specimen 

 from the Kimmeridgian of Hanover described by Struckmann\ 

 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 speci- 

 men and the mandible described above, I propose to designate them 

 both as H. major. Comparison cannot, unfortunately, be instituted 

 with Sapheosaurns, H. v. Mej., which agrees very nearly 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 pro- 

 bably be added, viz. the fuller ossification of the vertebral centra, 

 which appear to be less deeply excavated at either end than in Sphe- 

 nodon. All these cliaracters, except the absence of uncinate processes, 

 may be regarded as indicating a higher development hi the Rhyncho- 

 cephalian line. I hold that of the two most recent writers on the 

 ^ Zeitscbr. deutsch. geol. Ges. xxv. p. 249, pi. vii. (1873). 



