58 



MARINE AND FISHERIES 



1-2 EDWARD VII., A. 1902 



probably migrating rays moving up towards the girdle. ' In the effectual discharge of 

 the function of the fish's fin, increase of breadth is needed : and this increase of surface 

 is obtained by the gradual approximation of more and more lateral elements of the 

 archipterygium to the shoulder-girdle* was a characteristically apt observation of the 

 late Professor Huxley.' 



This brief description of the pectoral fins of Lamna, and the comparison made 

 between its skeletal structure, and that of certain other primitive fins of morphological 

 interest, it need hardly be pointed out, amply substantiates the point urged at the com- 

 mencement of this paper, viz : — the modification of the basal and radial cartilages for 

 the purpose of increasing the breadth and depth of the fin, and thus increasing the pro- 

 pelling capabilities of the limb. The shortening in longitudinal direction of the 

 basipterygium and its increase in compactness and strength, is accompanied by an 

 extraordinary lengthening of the free part of the fin, the slender cartilaginous rays being, 

 as before pointed out, remarkably long. 



Many interesting theoretical suggestions arise in the study of such a pectoral fin as 

 that of Lamna, but the limits of this report preclude any generalizations involving 

 lengthy references to the extensive existing literature, English and foreign, upon the mor- 

 phology of the paired fins in fishes. 



* Huxley "on Ceratodus forsteri" Proc. Zool. Soc, Jan., 1876, p. 55. 



EXPLANATION OF PLATES. 

 PLATE V. 



Fig. 1. Left pectoral fin of Lamna cornubica with muscles and integument removed. About one* 

 third natural size. 



PLATE VI. 



Fig. 2. Right pectoral fin of Lamna cornubica. About one-third natural size. 



PLATE VII. 



Fig. 3. Right pectoral fin of Scyllium after A. Milnes Marshall. 



Fig. 4. .i n Acanthias after Gegenbaur. 



Fig. 5. n .i Heptanchus after Wiedersheim. 



Fig. 6. i. « Chimcera after Bashford Dean, 



Fig. 7. " « Cestracion after Huxley. 



* Fig. 8. m u Polyodon after Huxley. 



Fig. 9. u m Baia radiata after A. T. Masterman. 



Pro. Propterygium. 

 Me sop. Mesopterygium. 

 Metap. Metapterygium. 

 a. Displaced anterior ray. 

 h. Horny fin-fibres. 



m. n. o. Probable separated nodules of adjacent rays. 

 Probable separated nodule from ray termination. 

 y. Main fin-ray of Metapterygium (according to Wiedersheim). 



