37. MKsonuoN. 197 



Miisouiii, fn>m the west coast of i\.frieii ; they roprcsont one or two 

 nominal sj)ecics of Valenciennes {M. </orcensis, and proljahly M. fal- 

 f/tt>i>) ; the females have a considerably more elevated body than the 

 males. 



y, B. Adidt : male. Elver Niger. From Jlr. Fraser's Collection. 

 €. Adult : female. River Niger. From Mr. Fraser's Collection. 

 ^. Adult : female. Coast of Africa. From the Haslar Collection, 

 j;. Htdf-grown. Fernando Po. From Mr. Fraser's Collection. 



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

 its extremity, and has the posterior margin convex and the anterior 

 concave. The posterior processes of the intermaxiLlary bones are of 

 moderate length, about two-thirds the length of the bones themselves ; 

 these are armed Avith a paii' of very strong canines, between wliich 

 are two other pairs of smaller ones ; there is a series of short conical 

 teeth along all the outer margin ; the remainder of the teetli form a 

 rillifonn band. The mandibulary is fiuTiished with an outer series 

 of conical teeth ; those standing in front of the jaw and in the middle 

 of the side of the dentary are the largest and canine-like ; the villi- 

 form band of mandibulary teeth does not extend on the lateral por- 

 tion of the dentary. The vomeiine teeth are arranged in an anchor- 

 shaped villiform band, which extends backwards to the middle of 

 the bone. The palatine teeth form a broad band, three times as long 

 as broad, wliich does not extend on the pterygoid. The turbinal 

 bones are strong, elongate, and being very divergent, they leave 

 between them a triangular groove, to receive the processes of the 

 intermaxUlaries. The anterior portions of the frontal bones also 

 diverge, and leave between them a space, tUled up by an elongate 

 portion of the ethmoid, which in this and other species of Mesoprion 

 forms part of the upper surface of the shuU. The space between 

 the orbits is rather narrow and flat, 'W'ith some grooves and openings 

 of the rudimentaiy system of muciforous channels. The portion of 

 the upper smface of the skidJ, behind the orbits, is distinguished by 

 high crests, lea\-ing between them very deep longituflinal grooves. 

 The median crest is that of the supraoccipital bone, which, strong, 

 but moderately elevated, slightly bifiuxatcs in front, and extends on 

 the frontal bones to above the middle of the orbit. Two other crests 

 arise from the orbit, the inner of wliich iiins (nearly parallel with. 

 that of the occipital bone) to the aiiiculation of the superior piece of 

 the supraseapula ; the outer crest descends do■v\^lwa^ds in a slight 

 curve, and terminates at the junction of the supraseapula, operculum, 

 and prajoperculum. The groove between the two outer crests is tri- 

 angular, and a large opening leads into the occipital region. The prffi- 

 orbital is largo, irregularly quackangular, and smooth ; the remainder 

 of the infraorbital bones are narrow, and form the base for a large 

 concave plate reaching into the interior of the orbit. 



The opercidimi has neither spine nor notch ; the sub- and intor- 

 operculum entire. The limbs of the prajoperculum have a \eiT oblique 

 direction towards eacli other ; the angle is rounded, and armed with 

 strong spinous teeth ; the posterior limb is minutely serrated in all 



