188 DE. W. G. RIDEWOOD ON THE CRAKTAL OSTEOLOGY OF 



On the Cranial Osteology of the Pishes of the Families 

 MormyridcB, Noto'pteridce and Hyodontidce. By W. Gr. 

 "RiDEWooD, D.Sc, F.L.S., Lecturer on Biology at St. 

 Mary's Hospital Medical School, London. 



[Bead 5t.h May, 1904.] 



(Plates 22-25.) 



The Morinyroid fishes have always been an interesting family, 

 and have, on the whole, probably attracted more attention than 

 auy similarly circumscribed and terminal group. Owing to 

 their freshwater habit and geographical limitations generally, 

 their evolution has been constrained, and limited in the main to 

 certain parts of their organization, with the result that they 

 exhibit a most curious medley of primitive characters coupled 

 with highly specialized and even degenerate characters. The 

 large size of the brain, the presence of an electric organ in the 

 tail, and the extraordinary shape of the snout in several of 

 the forms are indications of a high degree of specialization, yet 

 many of the other organs of the body show a retention of a 

 primitive condition. There seems to be good reason to believe 

 that the family branched off early from the lower Malacopterygian 

 fishes, and became a terminal group. Their nearest relatives 

 have generally been taken to be the Notopteridse, with the 

 Hyodontidse somewhat more remotely allied. The study of 

 the skull in the three families Mormyridse, Notopteridse, and 

 Hyodontidse forms the subject of the present communication. 



Eenewed interest in the Mormyridse has recently been evoked 

 by the discovery of a great many new forms in the Congo, 

 described by Boulenger in the following three works : — Proc. 

 Zool. Soc. 1898, pp. 775-821; Ann. Mus. Congo, Zool. i., 

 Bruxelles, 1898-1900 ; Les Poissons du Bassin du Congo, 1901, 

 Bruxelles, 8vo. It is to him that I am indebted for the material 

 examined during the course of the present investigation, and to 

 him I beg to ofi'er my sincere thanks. 



MOEMYRID^. 



The literature on the skull of Mormyroid fishes is not very 

 extensive. Gymnarchus has been fully treated of by Erdl 

 (Abhandl. Bayer. Akad. Wiss., v. 1. 1847), and Hyrtl 

 (Denkschr. Akad. Wiss. Wien, xii. 1. 1856). As regards the 



