26 MOEMTEIDiE. 



MALACOPTERYGXI. 

 MORMYRIDiE, 



Margin of the upper jaw formed by the single pragm axillary and the maxillaries, the 

 latter articulated above the former to the mesethmoid * ; parietal bones separating 

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

 the squamosal, the epiotic, and the exoccipital, covered by a large, thin, bony plate (the 

 supratemporal) ; symplectic absent ; suboperculum small and hidden under the 

 operculum, or absent. No pharyngeal teeth. Opercular bones hidden under the 

 skin ; gill-openings narrow. Anterior ribs sessile ; epineurals, no epipleurals. Pectoral 

 fins directed upwards. Ventral fins with 6 or 7 rays. Air-bladder communicating 

 with the ear. 



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

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

 usually few ; teeth usually present on the parasphenoid, working against a similar 

 patch on the tongue ; eye covered over by skin, or at least without free border, 

 sometimes very indistinct ; scales small, cycloid ; branchiostegal rays 4 to 8. 



In most of the genera the vertebral column must be divided into three principal 

 regions: — 1. The prsecaudal proper ; 2. An intermediate region with strongly developed 

 ribs attached to closed haemal arches, under which the posterior portion of the air- 

 bladder extends; 3. The caudal proper. The second region does not exist in 

 Mormyrops and Gymnarchns. The following is the number of vertebrae in the Nile 

 species examined by Hyrtlf and by myself: — ■ 



Mormyrops anguilloides 23-24 + 36-37 = 59-61. 



Petrocephalus bane 9 + 4-6 + 27-29 = 42. 



Marcusenius isidori . . . . . . 10 + 4 + 23 = 37. 



„ petherici 9 + 5 + 27 = 41. 



Gnathonemus eyprinoides . .... 13-14 + 6 + 29 = 48-49. 



„ tongibarbis 14 + 5 + 26 = 45. 



niger . . . . . . 10 + 6 + 25 = 41. 



Mormyrus hasselquistii 16 + 8 + 27 = 51. 



* For the nomenclature of the bones of skull, cf. Eidewood's valuable paper in Journ. Linn. Soc, Zool. 

 xxix. 1904, p. 188. 



t Benkschr. Ak. Wien, xii. 1856, p. 1 9 



