of the Tail in IcJdhyosauria. 439 



These vertebrae also make the joint in the fail at which th ; 

 antjular flexure commonly occurs in Lias specimens. 



The remainder of the tail in 0/'^<Aa^mosaMr«.9, as preserve 1, 

 comprises forty-one vertebrae, without any indication of the 

 end being reached. These vertebra are compressed fro^l side 

 to side and have the aspect of the bodies of dorsal vertel)r;e 

 of Teleosaurs or Plesiosaurs, the antero-posterior measure- 

 ment beini^ relatively long compared with the transverse 

 measurement. The centrum is free from lateral and inferior 

 processes, gives a strong attachment to the neural arch, and 

 has the articular faces moderately concave, but not approxi- 

 mating more than in many Plesiosaurs. Similar vertebrae 

 support the caudal fin found in German specimens from the 

 Lias. 



The first of the Oxford Clay fin-series is about 3 cm. high, 

 with a transverse width of about 2*6 cm. and antero-posterior 

 extent of 1'7 cm. Tiie size at first diminishes very slowly, but 

 more by a decrease in the height of tlie centrum than by 

 diminution in its length or width, though both of these vary. 

 The measurements at the twenty-seveiith centrum of this 

 series are antero-posterior 1*5 cm., transverse 1*9 cm., and 

 vertical 2 cm. The last vertebra preserved is I'l cm. long, 

 1"2 cm. wide in front and slightly less behind, and 1*2 cm. 

 high to the neural canal ; its posterior surface has a tendency 

 to convexity, and the process for the neurapophysis on the 

 right side is divided into anterior and posterior facets, as 

 though the nerve passed through the middle of the neuro- 

 central suture. The same condition is found in several of the 

 late vertebra, sometimes on one side, sometimes on the 

 other. Probably many vertebrae are missing from the 

 extremity of this tail. 



It thus appears probable that the number of vertebrae 

 supporting the caudal fin in Oxford Clay types exceeded 50 

 to 60. 



By the kindness of the late Professor Oscar Fraas 1 had 

 tiie opportunity of detailed examination of specimens from the 

 Lias of Germany in the Royal Stuttgart Museum. In the 

 specimen 3775 there are 101 vertebrae in the tail; caudal 

 ribs are only found in the first twenty-nine, so that 72 may 

 be regarded as supporting the caudal fin. The neural arch is 

 seen in all the caudals except the last twenty-two, though it 

 becomes very small, and the neural spine is short. 



In no. 8-4G there are 115 caudal vertebnv. Of these i^S are 

 posterior to the angular bend in the tail, and presumably 

 supported the caudal fin. 



29* 



