440 On the Extremity of the Tail in IcJithyosauria. 



No. 5792 is the Ichthyosaurus multiscissus (Quenst.). The 

 tail is 4 feet 9^ inches long and includes 108 vertebras, of 

 which the last 75 appear to have supported the caudal fin. 



In no. 5093, 127 caudal vertebrae are preserved, somewhat 

 scattered towards the terminal end, but upwards of 90 appear 

 to have supported the caudal fin. 



The specimen 5094, named /. tenuirosiris, which is only 

 3 feet 10 inches long, has 100 vertebrse in the tail, of which 

 the last 70 supported the caudal fin. 



I have a note of a specimen at Tiibingen in which the first 

 thirty caudal vertebrae have a length of less than 3 feet, and 

 the remaining eighty-three vertebrae a length of 2 feet 8 inches 

 in the region of the caudal fin. 



In the Tubingen specimen 10,999 about 70 vertebrse 

 support the caudal fin in a length of 2 feet. 



In Ichthyosaurus triscissus there are 83 vertebrge in the 

 tail, of which fifty are witiiout ribs and appear to have 

 supported the caudal fin ; and in no. 7532 there are 105 

 caudal vertebrae, but only twenty-two are posterior to the 

 angular bend in the tail. 



In 1881 Sir Richard Owen counted 60 vertebrse in the 

 deflected part of the tail in Ichthyosaurus tenuirostris. 



One of the most interesting specimens is in the Leicester 

 Museum marked 1892/4765, from Barrow-on-Soar. It is 

 the detached whip-like termination of the tail of an Ichthyo- 

 saur which appears to be perfect, though the vertebrae are 

 not absolutely free from a little matrix, which slightly masks 

 their articular edges. The vertebra are all exceptionally 

 short. The first three are relatively large and appear to be 

 from the position of the usual angular deflection. They are 

 followed by eighty vertebrae, which progressively decrease in 

 length and size and diminish till they become like coarse 

 granules which still retain the vertebral form. The terminal 

 vertebrae are smaller than in any other example of the caudal 

 fin series. 



The caudal fin series appear to be exceptionally long in 

 the British Museum specimen from Wiirtemberg, which 

 contains several embryos. 



It is thus evident that the number of these tail-fin vertebrse 

 is variable in tlie different species from the Lias. On the 

 whole the evidence appears to indicate that the caudal fin was 

 longer in most of the Liassic than in the Lower Oxfordian 

 types ; and although the fragmentary remains from the 

 Cambridge Greensand do not give any definite information, 

 they suggest the inference that in the Cretaceous types the 



