444 PROCEEDINGS OP THE ACADEMY OF 



Marcusenius Gill. 

 Marcusenius anguilloides = Mormyrus anguilloides Linn. 



Mormyrops Muller. 

 Mormyrops cyprinoides = Mormyrus cyprinoides Xinn. (nee Geoffroy.) 



Gnathonemus Gill. 

 Gnathonemus petersii = Mormyrus petersii Giinther. 



Hyperopisus Gill. 

 Hyperopisus dorsalis = Mormyrus dorsalis Geoffroy. 



Petrocephalus Marcusen. 

 Petrocephalus bane = Mormyrus bane Val. 



Isichthys Gill. 



Body anguilliform, with the height subequal as far as the caudal peduncle, 

 which is abruptly attenuated. Scales rather small. Head oblong, about 

 twice as long as high. Snout scarcely projecting, and convex. Mouth trans- 

 verse ; the periphery of each jaw convex in front. Teeth compressed and 

 with emarginated summits. Eyes small, considerably behind the vertical 

 from the mouth. Nostrils simple, small, two in a longitudinal line in front 

 of each eye. Dorsal fin elongated, nearly equalling half the total length, 

 separable from the back at the base of the membrane between the rays. Anal 

 fin rather shorter than the dorsal, coterminal with it and constructed at its 

 base like the dorsal. 



This genus is at once distinguished from all others of the family by the 

 elongation and comparative proportions of the dorsal and anal fins. The pe- 

 culiarity of the dorsal and anal fins recalls to mind the nearly similar char- 

 acter found in some of the Balistoidse, a coincidence which is the more notice- 

 able as the Mormyroids have also the upper maxillary bones united like the 

 Plectognathi. 



Isichthys henryi Gill. 



The greatest height equals a tenth (10) of the length {exclusive of the caudal 

 fin), and that at the ventrals an eleventh ('09) of the same; the latter is nearly 

 two times and a half as great as the height behind the vertical fins ('03J). 

 The head 1othe margin of the operculum forms almost a seventh (14) of the 

 length, and is twice as great as the height, or two times and a half as great as 

 that of the eye ("05 J). The eye is contained about ten times in the head's 

 length. The interorbital area rather exceeds a fifth ( - 03) of the same length, 

 while the length of the snout equals a fourth ( - 03). 



The dorsal fin commences considerably before the end of the anterior half 

 of the length (*45), and its own length equals half of the total (*50). The 

 greatest height equals that at the pupil (-05|); its posterior portion appears to 

 have been lower. The anal fin commences nearly even with the second half 

 of the length (51) or under the seventh or eighth dorsal ray, and is cotermi- 

 nal with the latter fin ; its height at the middle exceeds that of the dorsal 

 (O62) and at its produced and rounded posterior angle is still greater ( - 08). 

 The pectoral fin equals an eleventh of the length (*09) ; the ventrals are in- 

 serted near the end of the third tenth of the length (*38) and each one 

 equals two-thirds of the pectoral {'06). 



The scales are small, there being about 135 along the lateral line ; the 38th 

 to 41st is on the vertical from the ventral fin ; the 50th to 53d from the origin of 

 the dorsal, and the 64th to 67th from the anal. At the vertical of the origin 

 of the dorsal fin, there are twenty-six rows of scales, of which ten are above the 

 lateral line, and at that of the anal, twenty-one rows, of which nine are 

 above. 



[Sept. 



