THE ORDERS OF TELEOSTOMOUS FISHES 469 



but the supraoccipital has not yet displaced the parietals in 

 the median line. 



"The Albulidae are merely Elopine fishes with a forwardly 

 inclined mandibular suspensorium, a small mouth, and reduced 

 branchiostegal apparatus. Their primitive character is, indeed, 

 shown by the presence of a muscular conus arteriosus with two 

 rows of valves in the heart of the sole surviving species. 1 They 

 seem to differ from the Elopidse in exactly the same manner 

 as the more generalized Pycnodontidae differ from the Semi- 

 onotidae among Jurassic fishes. Now, however, the splenial 

 bone has disappeared, and is no longer available to bear a 

 powerful dentition. A new modification, therefore, occurs for 

 the first time, and is almost constantly repeated in later fishes 

 which have teeth on the palate or the base of the skull. This 

 upper dentition is henceforth usually opposed not to the mandible 

 but to a dental arrangement on the tongue or hyoid apparatus" 

 (A. S. Woodward 2 ). Among the Cretaceous Albulids, Istieus 

 is ancestral to the existing genus Bathythrissa, a long-bodied, 

 deep-sea form. The existing members of the Elopidse and 

 Albulidae undergo a developmental metamorphosis, the ribbon- 

 shaped larvae frequently being abyssal, like the larvae of Eels. 

 In both families the large maxillary is movably articulated above 

 the premaxillary to the ethmoid (Boulenger), and the jaws, oral 

 cavity, and throat are thickly studded with teeth. 



The Osteoglossidae are more specialized than the preceding 

 families in the union of the larger maxillaries with the pre- 

 maxillaries. The teeth, on the jaws, pterygoid and hyoid bones 

 are thickly clustered. The four existing genera parallel the three 

 existing genera of Dipnoi in habit and especially in distribution. 

 This probably indicates that the Osteoglossidae existed in the 

 Jurrasic, side by side with the widely dispersed Dipnoi, the 

 ranges of the groups being subsequently restricted pari passu. 

 The head is scaleless, protected by thick derm bones; the large 

 bony scales are composed of mosaic-like pieces. The huge Ar- 



»" J. E. V. Boas, ' Ueber den Conus arteriosus bei Butirinus und bei 

 anderen Knochenfischen, ' Morphol. Jahrb., Vol. VI, 1880, p. 528." 

 2 Catalogue of the Fossil Fishes in the British Museum, Pt. IV, 1901, pp. 

 vi, vii. 



