54 DR. W. G. RIDEWOOD ON THE CRANIAL [May 3, 



be restricted in the main to primitive features. There is no doubt 

 that the Elopidse are the most archaic of existing Teleosteans, and 

 that the AlbuHdse ai-e in few respects more highly speciahsed ; but 

 the study of the skull does not show any direct affinity between 

 the two families. There is no specialised character common to 

 both. Such resemblances as exist between them are explicable 

 by the fact that neither has depai'ted to any great extent from 

 the ancestral group from which all the Teleostean fishes sprang ; 

 and there is no evidence (from the study of the skull) that the 

 divergence of the two families fi'om a single one occurred at any 

 considerable height above the root of the phylogenetic tree. 



In the presence of conal valves of the heart other than those at 

 the junction of the conus with the ventricle (see Boas, Morph. 

 Jahrb. vi. 1880, p. 528), Alhula exhibits a character common in 

 Ganoid and still lower fishes, but not possessed by any other 

 living Teleostean ; while in the possession of a median jugular 

 or gular plate Ulops and Megalops exhibit a resemblance to the 

 Ganoid Amia which is not shared by any other Teleostean fish. 

 The Elopidse were abundant in Cretaceous times, and some of the 

 extinct forms would seem to be more specialised than the living 

 Elops and Megalops, since they exhibit a reduction in the size of 

 the jugular plate {Tlirissopater and Spaniodon) and a separation 

 of the two parietal bones [Rhacolepis, TJirlssopater , Spaniodon, 

 and others). (See Smith Woodward, Brit, Mus. Cat. Foss. Fish. 

 iv. Introduction, p. vi.) 



There is no instance among Teleosteans of a paired vomer such 

 as occurs in Amia and its allies, but it is worthy of note, perhaps, 

 that in Elops, and to a lesser extent in Megalops, the vomerine 

 teeth are disposed in two patches, right and left. 



Of the characters common to the skulls of the Elopidfe and the 

 Albulidse may be mentioned the small size of the parietal bones 

 and their meeting in the median line ; the roofing of the posterior 

 temporal fossee ; the presence of siibtemporal fossse ; the presence 

 of opisthotic, basisphenoid, and orbitosphenoid bones, an upper 

 and lower hypohyal on each side, and an ossified first pharyn go- 

 branchial ; the distinctness of the endosteal articular from the 

 ectosteal articvilar, and the fusion of the angular bone with the 

 latter ; and the presence of teeth on the dentary, premaxillary, 

 entopterygoid, and parasphenoid bones. 



Teeth occur on the vomer and palatine in Elops, Megalops, and 

 Albula, but not in Bathythrissa. Minute denticles occur on the 

 surface of the ectopterygoid in Elops and Megalops, but there are 

 none in Bathythrissa and only two or three small teeth at the 

 front of the ectopterygoid in Albula. The mouth in the Albulidfe 

 is reduced in size, and i~ts upper border is formed by the pre- 

 maxillse alone, the maxillse being toothless, whereas in the Elopidfe 

 the upper border is supported by both premaxillse and maxilla?, 

 and both bear teeth. There are two surmaxillse on each side in the 

 Elopidfe, and one in the Albulidfe. 



The mandibular suspensorium (hyomandibular and quadrate) is 

 slightly tilted forwards in Elops ; in Albula it is strongly rotated 



