354 Mr. C. T. Regan on the Caudal Fin 



Measurements of the type : — 



Head and body 160 mm. ; tail 125 ; hind foot 33 ; ear 20. 



Skull : greatest length 31*5 ; basilar length 28-2 ; nasals 

 13-3X4-6; interorbital breadth 4*8 ; breadth across parietal 

 ridges 11*2 j breadth of brain-case 14; palatal foramina 7; 

 diastema 9'2 ; palatilar length 16 ; length of bullae 6*8 ; 

 upper molar series 6*8. 



Hob. Gunnal, Portuguese Guinea. 



Type. Adult male. Original number 49. Collected 28th 

 July, 1909, by Dr. W. J. Ansorge. 



XLV1II. — The Caudal Fin of the Elopidas and of some other 

 Teleostean Fishes. By (J. Tate Regan, M.A. 



(Published by permission of the Trustees of the British Museum.) 



In the Jurassic and Cretaceous fishes of the family Oligo- 

 pleurida3 (Oligopleurus, Spathiurus, Oenoscopus) the caudal 

 fin was symmetrical in form but structurally beterocercal ; 

 the terminal portion of the vertebral column was rather gently 

 inclined upwards, the centra continued right to the bases of 

 the fin-rays, and a notochordal prolongation, perhaps invested 

 with cartilage, separated the epaxial and hypaxial rays, 

 which were sharply differentiated ; the series of spinous 

 epaxial rays comprised anterior rays which increased in 

 length backwards, and shorter posterior rays ; the former 

 bent forward below and were supported by a few (not more 

 than 4 or 5) basalia, whilst the rest were inserted on the 

 notochord or behind its termination on the uppermost hypaxial 

 ray ; the hypurals were numerous and but little expanded. 



In the PholidophoridaS the structure appears to have been 

 essentially similar, but the Leptolepidte were different and 

 had a caudal fin like that of the living Elopidaj. 



In Elops (affinis, machnata, and lacerta) and Megalops 

 (atlanticus and cyprinoides) the upturned portion of the 

 vertebral column is shorter and more abruptly inclined up- 

 wards than in the Oligopleuridje, and includes only three 

 centra; the last centrum is remote from the bases of the fin- 

 rays, and indeed the notochordal prolongation only separates 

 the lowest epaxial and uppermost hypaxial rays basally, 

 terminating in an opisthural cartilage. The posterior neural 

 arches, crowded together by the abrupt upturning of the 

 vertebral column, have taken on the function uf strengthening 



