MALACOPTERYGII 549 



Albula is represented in the Eocene (London Clay and 

 Bruxellian); and the Cretaceous Istieus and Anogmius are believed 

 to be possibly related to Ptcrothrissus. Four Cretaceous types 

 (Plethodus, Thryptodus, Syntegmodus, and Ancylostylus) are referred 

 with doubt to the Albulidae. 



Fam. 7. Mormyridae. Margin of the upper jaw formed 1 >y 

 the single praemaxillary and the maxillaries, the latter articulated 

 above the former to the ethmoid. Parietal bones separating the 

 supraoccipital from the frontals ; a large hole on each side of the 

 skull, between the squamosal, the epiotic, and the opisthotic, 

 covered by a large, thin, bony plate (the supratemporal), which 

 may extend over a part of the parietal ; sympleclic absent ; 

 suboperculum small and hidden under the operculum, or absent ; 

 interoperculum well developed. Basis cranii simple. No 

 pharyngeal teeth. Opercular bones hidden under the skin ; 

 gill-clefts narrow. Anterior ribs sessile ; epineurals, no epipleurals. 

 Pectorals directed upwards. VentraLs with 6 or 7 rays. Air- 

 bladder communicating with the ear. 



FIG. 329. Mormyrus caballus. nat. size. 



Curious-looking Fishes, very variable in the form of the head 

 and body and in the extent of the fins. Mouth often very small ; 

 teeth in jaws usually few; teeth usually present on the para- 

 sphenoid, working against a similar patch on the glossohyal ; eye 

 covered over by skin, sometimes very indistinct ; scales small, 

 cycloid ; branchiostegal rays 4 to 8. The dorsal and anal fins 

 may be nearly equally developed (Genyomyrus, Gnathonemus) ; or 

 the former (Mormyrus) or the latter (Hyperopisus) are several times 

 the longer. Gymnarchus, Eel-shaped, apodal, and deprived of the 

 caudal fin, lacks the anal fin, the dorsal extending over the whole 

 extent of the body. Some species of Mormyrops show how a form 



