258 THE ZOOLOGIST. 



slightly concave on the outer face, coming to a point at the 

 posterior end, and having, in the specimen obtained, on the 

 lapillus from the right side of the head an excrescence like a 

 minute hillock in the concave plain at the anterior end. In 

 another specimen, in the Royal College of Surgeons Museum, 

 this minute hillock has a hook-like shape. The otoliths in these 

 specimens are of a very chalky texture, and the markings do 

 not show very plainly. 



Next in order may be taken those fishes in which the lapillus 

 is the largest of the three otoliths on one side of the head ; this 

 occurs in the Mormyridce, Hyodontidce, Siluridce, and Loricariidce. 

 Beginning again with those that have the largest lapillus, the 

 first family to be described is the Siluridce or Catfishes. 



Siluridjs. 

 In the marine members of this group the lapillus is a really 

 big stone, whilst some of those living in fresh water have, for 

 the size of the fish, a very small one. A contrasting instance is 

 given in the ' Zoologist ' for January, 1915. The lapillus of 

 Arius buchanani (fig. 2) is a large stone ; it is the same with all 

 the Ariidce and the allied genus JElurichthys. The lines of 

 growth in the specimen figured, and also in others of the family, 

 are plainly visible owing to the size of the stone. In other 

 fishes, the stone being small, these lines do not show as a rule. 

 A. gagora has a large stone semi-globular as to one-half, the 

 other half stretched out at its outline and coming to a blunt 

 edge. JElurichthys gronovii has a stone with one part of its 

 outline projecting into a distinct point. Platystoma fasciatum 

 also has a large lapillus (fig. 3) differing considerably in shape 

 from those of the Arius family. The lapillus of Bagarius 

 yarrellii, a fish found in the rivers of India, is particularly small 

 viewed in relation to the size of the fish. Synodontis schall, a 

 Siluroid from the Nile, has but a small lapillus. 



Moemyridje. 

 Mormyrus kannume (fig. 4), a fish from the Nile, has a 

 lapillus of a roughly circular outline, although it is the largest 

 of its three otoliths ; it is moderate in size considering the size 

 of the fish. 



