FINS OF ELASMOBKANCHS. 453 



The Pectoral Fin (Plate LXXVIII. fig. 1). 



In this fin the mesopterygium is absent or defective, as there is a certain interspace 

 left between the metapterygium (c) and the larger basal cartilage. This larger cartilage 

 (which should probably be reckoned as both meso- and propterygial) is greatly ex- 

 panded distally, and is the main solid constituent of the limb. On its preaxial side is a 

 single elongated cartilage, somewhat broadest proximally, which may be the proptery- 

 gium, or answer to the preaxiad upcreeping radials which are found in Chiloscyllmm and 

 GingJymostoma. The proximal ends of the three most preaxial of the undoubted radials 

 have coalesced into a single plate. The radials of the postaxial part of the limb are 

 very irregularly arranged and segmented, and have, in part, coalesced into two plates, 

 placed close to the distal postaxial angle of the metapterygium, projecting postaxiad 

 much beyond it. 



The whole skeleton projects a little more distally on the postaxial than it does on the 

 preaxial side of the limb ; but the fin-rays project more on the preaxial side. 



The Caudal Fin (Plate LXXVIII. fig. 3). 

 The skeleton of this fin shows the same discrepancy between its dorsal and ventral 

 supports as has been before noted in other species. Ventrally there are cartilages 

 numerically corresponding with the vertebrae, whence they continuously proceed. Dor- 

 sally the cartilages are separate, and have no definite numerical correspondence with 

 the subjacent vertebrae, which they much exceed in number. 



PRISTIS CUSPIDATA. 



First Dorsal Fin (Plate LXXVIII. fig. 4). 



The dorsal fin of this form is supported by large cartilaginous plates, which are in 

 series with other narrower superaxial cartilages situated more preaxially. The hindmost 

 and longest cartilages are separated proximally by a membranous interval. Distally 

 they support a series of twenty elongated, slender, unsegmented cartilages. 



The more postaxial of the two large basal cartilages appears to be segmented off from 

 the vertebra subjacent ; but the more anterior is intimately united with the axial 

 skeleton beneath. 



The large basal cartilages seem to correspond with the median and basal series of 

 cartilages of those dorsal fins which have three superimposed series of cartilaginous 

 elements, or, if not to both, certainly to the basal series, and therefore to the conti- 

 nuous basal cartilage, of the dorsal fin of Notidanus. 



RHYNCHOBATUS DJEDDENSIS. 

 Dorsal Fin (Plate LXXVIII. fig. 5). 

 The first dorsal of this species presents a series of eighteen moderately elongated 

 juxtaposed radial cartilages, which descend to unite with the skeletal axis. What is 



