196 DR. W. a. EIDEWOOD OK THE CRANIAL OSTEOLOGY OP 



bone, rougUy square in outline ; the third is a slightly curved, 

 forwardly directed rod, which is attached to the posterior end of 

 the second pharyngobranchial, and not, as is more usual, to the 

 mesial edge of its anterior end. 



Other MoRMYRiD^. 



The skulls oi Mormyrops and Petroceplialus just described were 

 specially prepared for the purposes of this investigation from 

 alcohol-preserved material kindly furnished by Mr. Gr. A. 

 Boulenger ; but for comparison with them I have been glad to avail 

 myself of ready-prepared skulls of five other genera of Mormy- 

 roid fishes from the Osteological Collection of the British Museum. 



Two species of Mormyrus were examined, Mormyrus cascliive 

 (a complete specimen, Brit. Mus. No. 1441, Nile ; and a large 

 fragmentary skeleton, also from the Nile), and Mormyrus Jiassel- 

 quisti (Brit. Mus. No. 879, Fashoda). The general aspect of 

 the skull is the same as that of Mormyrops, but parasphenoidal 

 teeth are well developed, and there are distinct prefrontal bones ;. 

 the orbitosphenoid has the appearance of being completely 

 divided into a right and a left part, but without cutting the skull 

 I am unable to make a definite statement on this point. The 

 dentition of the premaxilla and dentary is more feeble *, and the 

 teeth are bifid at the tip, like those of Petroceplialus. The 

 maxilla is of remarkable shape (PI. 23. fig. 10) in consequence 

 of the exceptional size of the horizontal, posteriorly directed 

 process a. The mandibular rami are much longer and narrower 

 than in Mormyrops and Petrocephalus. 



The relations of the hyopalatine arch are similar to those of 

 Mormyrops, but in Mormyrus cascliive there arises from the 

 postero-dorsal part of the pterygoid (probably the ectopterygoid, 

 but as there is no recognizable entopterygoid it is difficult to say 

 for certain) a process of bone which is united by a jagged suture 

 with the antero-ventral part of the orbitosphenoid. In Mormyrus 

 Tiasselquisti there is but the feeblest suggestion of such a 

 connection. 



The horizontal limb of the preopercular is approximately as 

 long as the upright limb, the two being set at an angle^^'of about 



*■ Boulenger (Proc. Zool. Soc. 1898, p. 780) employs this as a distinctive 

 character, Mormyrops and Petroceplialus having 12 or more teeth in each jav? 

 (upper and lower), whereas all the other genera (except Gymnarclms) have not 

 more than 10 teeth in each jaw. 



