of the Clupeidse and the Teleostean Urostyle. 533 



to add to Mr. Newton's very full and accurate description 

 but as his figure does not show quite clearly the precise limits 

 of the uroneurals I have made another drawing (fig. 2). The 

 principal differences from the adult Chatoessus are that the 

 uroneurals are more slender, the penultimate centrum is 

 distinct from the fifth hypural, and the last centrum is 

 segmented into three, clearly showing that the paired poste- 

 rior processes already described represent two incomplete 

 centra. 



Fiar. 2. 



Skeleton of caudal fin of a young' Clupeq. 

 Lettering as in Fig. 1 . 



The name " urostyle " has not usually been applied to any 

 of the pairs of bones (uroneurals) which protect the terminal 

 part of the notochord in the Clupeidae and many of the more 

 generalized Teleosts, but has been used to designate the 

 continuous styliform bony investment of the end of the noto- 

 chord in Gastrosteus and in some other fishes. A comparative 

 study leaves no room for doubt that in many cases the 

 urostyle is merely the result of ankylosis of the uroneurals 

 and that centra take little or no part in its formation, and I 

 do not think that there are any fishes in which a urostyle has 

 been formed simply by ankylosis of posterior centra ; but that 

 is a matter which requires further investigation. However, 

 there can be no question that in the Clupeidas there is no 

 urostyle and that the bones so named by Mr. Whitehouse are 

 not derived from centra, but are the anterior of a series of 

 three pairs of bones, the uroneurals, which may be regarded 

 as neural arches pertaining to posterior centra which have 

 aborted. 



