1. LAEIMUS. 267 



c. Half- grown. River Niger. From Mr. Fraser's Collection. 



d. Adnlt : skeleton, lliver Niger. From Mr. Fraser's Collection. 



Pseudobranchiae well developed. Air-bladder simple. 



Skeleton. — The maxillary bone gradually widens from the base to 

 its extremity, which is not veiy broad. The intermaxillary is rather 

 slender, tapering to a very fine point, and is armed in all its length 

 with a narrow band of fine villiform teeth, and with an outer series 

 of more distant and very small teeth ; its posterior processes extend 

 backwards to the level of the anterior margin of the eye, being one- 

 third only of the length of the bone ; there is, besides, a flat trian- 

 gular process nearly in the middle of its posterior margin. The mu- 

 ciferous channel of the mandibulary is not very deep, and divided 

 into four cavities by three feeble bony cross-bars. The tympanic 

 and pterj'goid bones have a more solid osseous centre, and the rest 

 exceedingly thin and fragile. The anterior portion of the vomer is 

 triangular, excavated, with rather projecting anterior edges ; the 

 posterior is veiy feeble, tapering to a long, fine point. 



The bony ridges and crests at the upper surface of the skull are 

 peculiarly arranged. The occipital crest is very elevated above the sur- 

 face of the skull, and its horizontal portion is rather higher than the 

 vertical ; it does not extend beyond the sujirascapula. There is no 

 central cavity, but all the cavities are arranged in pairs. The first 

 pair occupies the anterior portion of the fi'ontal bones ; the second is 

 situated more in the centre of the distance between the eyes, and 

 occupies the middle of the fi-ontals ; the third and fourth are elon- 

 gated, and placed more outwards, the latter immediately above the 

 upper posterior angle of the eye. There is a wide space between the 

 cavities of the third pair- and the occipital crest, unoccupied by mu- 

 ciferous channels. The third and fourth pair are continued into the 

 channels of the infraorbital bones and of the suprascapula. The 

 prajorbital is narrow, about thi-ee times as long as broad, and has 

 foiu- or five grooves. The turbinal bone is transformed into a half- 

 channel of moderate length. There are four grooves between the 

 ridges of the prteopcrculiuu ; they are wide, not deep, and separated 

 from one another by narrow bony cross-bars. Only the angle of the 

 bone is distinctly serrated, the inferior limb exhibiting some obsolete 

 denticulations ; the posterior is entirely smooth. The operculum has 

 a deep angular notch, and no prominent spines, nor a ridge on its 

 interior surface ; the suboperculum is slightly notched before the 

 base of the pectoral fin ; the suprascapula is entii'e. 



The lower part of the skull is veiy much swollen, globular, with 

 a narrow groove along the medial Hue. 



The glossohyalis styHform, and rather broader anteriorlj'; the lu'o- 

 hyal is an elongate triangular plate, with a groove along its inferior 

 margin. The pubic bones have no posterior process, and are diver- 

 gent anteriorly. 



There are eleven abdominal and fifteen caudal vertehra, the 

 length of the former portion of the column being to that of the 

 caudal as 1 : 1-26. The first interha;mal spine is rather strong, and 

 equals the length of the second vertebra to the sixth. 



