XXI MALACOPTERYGII 549 
Albula is represented in the Eocene (London Clay and 
Bruxellian); and the Cretaceous /stiews and Anogmius are believed 
to be possibly related to Pterothrissus. Four Cretaceous types 
(Plethodus, Thryptodus, Syntegmodus, and Ancylostylus) are referred 
with doubt to the Albulidae. 
Fam. 7. Mormyridae.—Margin of the upper jaw formed by 
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; symplectic absent ; 
suboperculum small and hidden under the operculum, or absent ; 
interoperculum well developed. Basis craniu simple. No 
pharyngeal teeth. | Opercular bones hidden under the skin; 
gill-clefts narrow. Anterior ribs sessile ; epinetrals, no epipleurals. 
Pectorals directed upwards. Ventrals with 6 or 7 rays. <Air- 
bladder communicating with the ear. 
Fic. 329.—Mormyrus caballus. +4 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, 
eycloid; branchiostegal rays 4 to 8. The dorsal and anal fins 
may be nearly equally developed (Genyomyrus, Gnathonemus) ; or 
the former (Mormyrus) or the latter (//yperopisus) 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 
