by william a. haswell, m.a., b.sc. 103 



Pectoral Fins. 



The pectoral arch is characterised by the solidity of its structure 

 and the massiveness of its lateral portions. The upper and lower 

 nerve-foramina are very large ; thei'e are no accessory foramina as 

 in Trygonorhina. ThB articular surfaces for the fin are placed on 

 a horizontal ridge, at the extreme anterior and posterior ends of 

 which are placed the surfaces for the propterygium and the metap- 

 terygium respectively ; the former is a long oval with the long axis 

 vertical and the surface directed outwards ; in the intermediate 

 ridge is a concavity for the mesopterygium. Close to the inner 

 lateral border of the arch is the articular surface for the fifth 

 branchial arch, which is double and somewhat raised above the 

 general surface. The propterygium has articulating with its distal 

 extremity a stout ray with which are connected a number of fin 

 rays. The mesopterygium is very small but occupies all the interval 

 between the propterygium and the meta pterygium; none of the rays 

 articulate directly with the shoulder girdle. The ru eta pterygium 

 is divided into four segments. 



The pelvic arch is a strongly curved cartilage which is produced 

 behind over the acetabular facet into a strong spine ; a little in 

 front of this it develops a prominent angular ridge on its outer 

 surface. The metapterygiurn bears distally two very short cartilages 

 which continue the axis of the fin and give origin to a few short 

 rays ; the mesopterygium is not represented. 



UROLOPHUS, sp. 1 



Plate II., Fig. 14. 



The main difference between the skeleton of this species and that 

 of Trygon pastinaca consists in the presence between the nasal 

 cartilages of a pair of very slender, crescentic, cartilaginous cornua, 

 attached to, but not continuous with, the cartilage of the front of 



