PROF. M. G. 6EELEY ON SAUK0DE8MUS EOBERTSONl. 1G7 



bone is Cholonian, it cannot be referred to an existing type, and 

 may be either a humerus or a femur. 



There is in the mutilated proximal end of the bone some resem- 

 blance to a mammalian femur, such as that which I described from 

 Stonesfield *, but the distal end of the bone forbids a comparison. 

 And it is as certainly not the femur of any reptile. I am not 

 familiar with any Chelonian in which the femur closely resembles 

 the humerus. The bone is, I submit, a right humerus, but the 

 characters have not hitherto been enunciated which would refer the 

 bone to the Chelonia. 



The characters which suggest Chelonian affinities have little value 

 in classification. They are limited to the general form of the bone. 

 The proximal end is expanded, with a saddle-shaped ventral surface, 

 but this condition occurs in OTm\h.ossiXiTs,mIIyperodapedon, and many 

 extinct genera of reptiles. The distal end and the articular head 

 of the bone appear both to be in the same plane, so that there is no 

 twist in the shaft ; but since the head is not preserved, it is not 

 impossible that it may have formed an angle with the distal articu- 

 lation. 



I am indebted to Mr. Boulenger for the opportunity of examining 

 bones of recent Chelonia in the British Museum, but I have found 

 no evidence to sustain the Chelonian hypothesis, nor any closer 

 resemblance than is seen in the right humerus of the genus 

 Hardella. 



Among the characters which I believe to constitute differences from 

 Chelonians are (1) the cellular medullary cavity in the shaft of the 

 bone, w^hich is filled with calcite ; for I am not aware that the humerus 

 is hollow in any Chelonian; (2) the straight shaft is unparalleled in any 

 Chelonians in which an approximate comparison could be made, for 

 they have the superior contour convex, and the infero-posterior 

 contour concave ; (3) the remarkably open concave curve between the 

 radial and ulnar crests is not paralleled in Chelonians, which have the 

 more or less lamellar, sub-triangular, radial crest close to the head 

 and reflected downward ; (4) the radial crest is distinct from the head 

 of the bone, does not extend so far proximally, and is relatively 

 small, as in no Chelonian ; (5) the slight development of the ulnar 

 crest, the rough muscular attachment along its extent, and its 

 convex contour in length are unknown among Chelonians ; (6) the 

 thickness of the ridge by which the shaft appears to have united 

 with the articular head in the fossil is greater than among Chelo- 

 nians, and it is possible that the shaft had an appreciable extension 

 proximally beyond the fracture which limits its preservation ; (7) 

 the transverse curved ridges on the ventral side of the head from 

 the radial process to the ulnar crest are distinct in their divergence 

 from the not dissimilar ridges sometimes seen on the Chelonian 

 humerus ; (8) the distal end of the shaft is unlike Chelonians in 

 the great transverse extent, in the flattening of the ulnar side of 

 the bone, which is concave in length, in the compression of the 



* Quart. Joiini. Geol. Soc. vol. xxxv. (1879) p. 456. 



