THE MOEMYBIDiE, NOTOPTEKIDJ*;, AND HYODONTID^. 189 



other Mormyroids, Heusinger gives a couple of figures, rather 

 crude, o£ the skull of Mormyrus cyprinoides in liis paper on tlie 

 auditory mechanism of certain fishes (Arch. f. Anat. u. Phys., 

 1826, pi. iv. figs. 8 & 9), but the standard work of reference is, 

 of course, Marcusen's monograph (Mem. Acad.Sci.St. Petersb., 

 ser. 7, vii. 4. 1864). Marcusen did not include observations 

 on Qymnarclius in this work. 



MOEMTROPS DELICIOSUS. 



Cranium (PI. 22. figs. 2 and 3). — The cranium is long, and 

 tapers uniformly in an anterior direction almost to a point. The 

 mesethmoid is low, and slightly bifid at the end. The vomer is 

 small and edentulous, and is fused at its sides with the inner 

 faces of the two palatine bones. Beneath the orbital region the 

 parasphenoid has a slightly concave nnder surface, with vestiges 

 of teeth close to the middle line. It is exceptionally broad just 

 in front of the pro-otic bones, but narrows rapidly behind this, 

 and terminates in a pair of narrow splinters of bone closely 

 applied to the ventral surface of the basioccij)ital. The eye- 

 muscle caual does not open posteriorly. 



There is no opisthotic. The supraoecipital has a well- 

 developed crest. The two parietals are fairly large, and meet in 

 the median line by an extensive suture ; the frontals are much 

 elongated. Lying below the epiotic ridge and above the 

 squamosal ridge is a large lateral foramen, occupied in nature by 

 a thick-walled spherical vesicle, but opening in the dried skull 

 directly into the cavum crauii. The foramen is bounded by the 

 squamosal, epiotic, and exoccipital bones *. 



The two alisphenoids are widely separated throughout, and are 

 much drawn out in an antero-posterior direction. Lying in 

 front of the alisphenoid, and touching it above the horizontally 

 elongated optic foramen, is a bone which can only be identified 

 with the' orbitosphenoid. It is in extensive union with the 

 parasphenoid below and the frontal above, and its transverse 

 width is greater than its height. The cranial cavity extends 

 into it, and the bone would be separated into a right and a left 

 half were it not that the two parts are connected by a thin 



* Boulenger's description of the lateral foramen of the Mormyroid skull 

 (Les Poissons dii Eassin du Congo, 1901, p. 49) as between the parietal and 

 opisthotic is incorrect, for the opistliotic is wanting in all Mormyroids and 

 the parietal is in all cases separated from the foramen by the squamosal. 



