of some Teleosiean Fishes. 



355 



the upturned vertebrse, thus replacing and inducing the 

 abortion of the posterior centra ; these neural arches have 

 become enlarged and have shifted their proximal attachments 

 downwards and forwards ; one is united by suture with the 

 centrum of the third last vertebra, and usually appears forked 

 at the base, the anterior fork running forward to the centrum 

 of the fourth last vertebra; the forking indicates the com- 

 pound nature of this bone, and in some specimens the line of 

 junction between the two component elements can be clearly 

 seen ; another bone is united to the posterior edge of the one 

 just described, and is prolonged upwards above it, and this is 



Fig. 1. 



Skeleton of caudal fin of Mops (somewhat diagrammatic). 



n, neural spines ; ep, epaxial basalia ; u, uroneurals ; hy, hypurals ; 

 h, haemal spines. 



also composed of two, the suture between which may persist, 

 so that we are here dealing with at least four posterior neural 

 arches, which I propose terming ' uroneurals' ; these are to 

 be regarded as pertaining to centra which have aborted, and 

 thus correspond to the posterior hypurals. The neural arch 

 of the actual last vertebra is expanded to form a plate, and 

 the shape and position of this and of the one or two arches in 

 front of it appear to be determined by the room required by the 

 epaxial basalia, now three in number. There are nine hypurals 

 or expanded hsemal spines, and three more haemal spines 

 also support the caudal fin. 



