.ETHALION. 125 



It may he added that in one of the specimens figured (PL XXIII, fig. 5, c.) the 

 intestine is conspicuous, filled with white faecal matter. 



Immature Fishes. — The type specimen of the so-called Leptolepis unmix, which 

 is re-drawn enlarged in PL XXIII, fig. 2, is obviously an immature example of 

 Leptolepis much shortened by distortion, and there is nothing to distinguish it 

 from L. brodiei. Below and in front of the large orbit, which is stained black, the 

 characteristic dentary bone is conspicuous. The telescoped vertebras irregularly 

 overlap, but the crushed dorsal and pelvic fins remain almost in their natural 

 relative positions. The base of the caudal fin is widened by the distortion. 



There can also be no doubt that the immature fishes named Oxy gonitis tenuis 

 by Agassiz are very young individuals of Leptolepis, almost certainly of L. brodiei. 

 Their relatively large and delicately ossified vertebral column is a well-known mark 

 of immaturity. 1 The type specimen, which is re-drawn enlarged in PL XXIII, 

 fig. 1, is made a little slender by crushing, but not otherwise distorted. Its skull 

 is missing, but the orbit is marked by a black stain, and the characteristic jaws are 

 seen. The relative width of the opercular apparatus is also clear. The feebly 

 ossified vertebral centra, in close series, are much deeper than long, not constricted, 

 and apparently about 40 in number. Slight traces of the pectoral fins and the 

 small remote anal fin are preserved, while the dorsal and pelvic fins are nearly 

 complete, though depressed by crushing. The large forked caudal fin is also well 

 displayed. Among other specimens labelled by Brodie, one in a group in the 

 British Museum (no. P. 70o4) exhibits very clearly the ascending process of the 

 dentary bone, and others show that the fins must have been as in L. brodiei. 



Horizon, and Locality. — Lower Purbeck Beds : Vale of AVardour, Wiltshire. 



Specifically indeterminable fragments of Jjeptolepis have also been found in the 

 Wealden. Among them may be specially noted the dentary bone of the mandible 

 shown enlarged in PL XXI II, fig. 7. 



Genus JETHALION, Minister. 

 Jtthalion, G. von Mhnster, Neues Jahrb. f. Min., etc., 1842, p. 41. 



Generic Characters. — As Leptolepis, but dentary bone of mandible gradually 

 deepening from the symphysis backwards without any marked thickening, and 

 vertebral centra much strengthened by secondary ossification in fine longitudinal 

 ridges. 



'/'///»■ Species. — Mthalion hnorri (Clupea hnorri, H. D. de Blainville, Nouv. 

 Diet. d'Hist. Nat., vol. xxvii, 1818, p. 331), from the Lower Kiinmeridgian (Litho- 

 graphic Stone) of Bavaria. 



1 W. C. Mcintosh and A. T. Masterman, The Life-Histories of the British Marine Food-Fishes 

 (1897), p. 415. 



