■436 MR. J. W. HULKE ON THE SKELETAL [NoV. 20, 



transverse processes are dwarfing, and they are borne wholly on 

 the neurapophysis distinctly above the neural suture ; no trace of 

 sutural attachinent of the transverse process is here discernible, and 

 the process appears to be an outgrowth from the arch. Vertebrae 

 posterior to the above are devoid of the transverse process ; their 

 centrum retains the flattened angular form, their spinous process 

 is more comjiressed, and its antero-posterior dimension is relatively 

 greater than in the corresponding vertebrae of Metriorhynchus. 



Sacrum. — The two sacral vertebrae differ so much from those of 

 Metriorhynchus that they require detailed notice. 



1st Sacral (fig. 6, p. 435). The centrum has a subcylindric shape. 

 In its anterior half tlie transverse horizontal dimension is enlarged 

 by the attachment of the transverse process. The anterior terminal 

 surface has an obtusely elliptic outline, of which the longer diameter is 

 horizontal. Its surface is distinctly concave in the horizontal and 

 nearly plane in the vertical direction. The lateral lip and the 

 adjoining part of this surface is contributed by the root of the stout 

 transverse process, and between the upper limit of this and that part 

 of the circumference which bounds the neural canal the lip of this 

 surface is formed by the neurapophysis. The transverse process 

 consists (1) of a large, stout piece of rudely trihedral, slightly fluted 

 cross section, directed nearly horizontally outwards. This is 

 suturally attached to the entire height of the side of the centrum in 

 the anterior half of this latter. Upon the upper surface of this part 

 of the process there descends from the neurapophysis a minor, thin, 

 splint-like part which ends with a serrated margin at a little distance 

 from the arch. The posterior surface of the centrum is nearly 

 circular in outline and nearly plane. 



2nd Sacral vertebra. Its sacrum is cylindroid. The anterior 

 face is nearly plane, its outline circular. The posterior face is larger ; 

 its outline is less elliptic and more nearly circular than is the anterior 

 face of the 1st sacral vertebra. It is nearly plane in the vertical and 

 distinctly concave in the horizontal direction. Its transverse process 

 is suturally attached to the whole vertical extent of the lateral sur- 

 face of the centrum. This attachment is separated by an interval 

 from both ends of the latter, the terminal surfaces being formed of 

 centrum only. The structuial plane of the transverse process 

 resembles that of the 1st sacral vertebra. Thus the sacral transverse 

 processes rank in respect of their chief component element as ribs, so 

 agreeing with those of Metriorhynchus ; and this remark applies also 

 to the transverse processes of the anterior caudal vertebra. 



Compared with that of Metriorhynchus, the sacrum in Sieneo- 

 saurus differs notably in the more nearly horizontal direction of 

 the transverse processes, which are also stouter and relatively shorter 

 The concavity of the anterior face of the first, and that of the pos- 

 terior face of the centrum of the second, sacral vertebra is less than 

 that of the same faces in Metriorhynchus, and the composition of 

 ■ these faces is also different. 



(No part of the pectoral girdle or fore limb has been yet procured 

 by Mr. Leeds.) 



