THE arOBMYEIDiE, NOTOPTERID^, AjSTD HTODONTID^. 197 



105 degrees ; and about one-half of the interopercular is visible 

 in an external view of the skull below the lower edge of the 

 preopercular. The ceratohyal is relatively shorter and stouter 

 than in Mormyrops, and the dentigerous membrane-bone longer 

 and more strongly toothed; but the essential features of the 

 hyobranchial skeleton are the same in both. 



Prepared skulls of Marcusenius isidori (Brit. Mus. No. 796, 

 Nile), and Gnatlwstomus cyprinoides (Brit. Mus. No. 1210, Nile) 

 were also examined, but no new features of interest were 

 discovered. 



Syperopisus hebe (Brit. Mus. Mormyrus dorsalis, 62.1.17.76, 

 Khartoum) is remarkable for the great developmeat of the para- 

 sphenoid and hyobranehial dentition. The teeth are flat-topped, 

 and are closely set in the form of a pavement. Both upper and 

 lower patches of teeth are of considerable breadth, and form a 

 very efficcient crushing apparatus. 



Two skulls of Gymnarchus niloticus * were examined, one 

 about 10 inches long, and the otber (Brit. Mus. 91.4.2.26, Lagos) 

 about 4^ incbes. The skull of Gyonnarclius has been so well 

 figured by Erdl (Abbandl. Bayer. Akad. Wiss. v. 1. 1847, pi. 5) 

 and Hyrtl (Denkschr. Akad. Wiss. Wien, xii. 1. 1856, pis. 1 

 & 2), that a bare description will bere suflice. Unfortunately 

 the figures of Hyrtl are not lettered, but the numbers attached 

 to the parts in Erdl's figure will serve in the subjoined remarks 

 for the recognition of bones, although the names which lie 

 gives to the bones are now obsolete. Marcusen did not in- 

 clude observations on Gymnarclius in his monograph on the 

 Mormyridse. 



The cranium is long, and the mesethmoid low. There is no 

 supraoccipital crest ; the parietals meet ; there is no opisthotic. 

 The lateral cranial foramen of Gymnarclius should rather be 

 described as a hemispherical depression, from the depths of 

 which three apertures lead into the cranial cavity. Its margin is 

 formed by the exoccipital, epiotic, and squamosal as in other 



* Although the skull, and particularly the branchial skeleton, of Gymnarchus 

 possesses some very remarkable features, I am disposed to follow G-unther 

 (Study of Fishes, 1880, p. 626) and Boulenger (" Eevision of the Mormyrida,' ' 

 Proc. Zool. Soe. 1898) in retaining the genus in the family Mormyridaj, rather 

 than to accept the earlier view of Griinther (Brit. Mus. Cat. Fishes, vi. 1866, 

 p. 225), and of Cope (Trans. Amer. Phil. Soc, n. s. xiv. 1871, p. 454), that it 

 should constitute a separate family, the Gymnarchidse. 



