A SYNOPSIS OF THE FISHES OF THE GENUS MASTACEMBELUS. 



By George A. Boulenger, D.Sc, Ph.D., F.R.S. 



The genus M astacembelus , forming with Rhynchobdella the very natural 

 family M astacembelidce , is characterized among Acanthopterygians by an eel-like 

 form, by the absence of ventral fins, by the position of the anterior nostril widely 

 separated from the posterior and opening in a tentacle on each side of a dermal 

 rostral appendage, and especially by the peculiarity of the shoulder-girdle, which 

 is not suspended from the skull, a character which is shared by the true eels. 



This is one of the genera our knowledge of which has been enormously 

 increased within the last few years by the exploration of the fresh waters of 

 Africa. When the last account of it was published in Giinther's Catalogue 

 of Fishes, Vol. Ill (1861), only eight species were known — seven from the Indian 

 Region, and one from the Euphrates. We are now acquainted with forty-five 

 species, which are distributed as follows: 30 from tropical Africa, 12 from S. E. 

 Asia (Indian or Oriental Region), 2 from S. W. Asia (Euphrates and Oxus), and 1 

 from China ( Yangtse-kiang) . 



The descriptions of these forty-five species, twenty-seven of which have been 

 named by myself, are at present scattered through a great number of books and 

 periodicals, and some of the older diagnoses fail to furnish the characters re- 

 quisite for their proper identification. I have therefore thought it would be 

 useful to avail myself of the large collection in the British Museum for drawing 

 up a key to the identification of the species, of which a list, with the necessary 

 synonymy, is appended. 



In dealing with the distribution of fresh-water fishes in his Introduction to 



the Study of Fishes (1880), Gunther has observed that "as a general 



genus or family of fresh-water fishes is regularly dispersed and most developed 

 within a certain district, the species and individuals becoming scarcer towards 

 the periphery as the type recedes more from its central home, some outposts 

 being frequently pushed far beyond the outskirts of the area occupied by it." 

 And further on he writes : ' ' M astacembelus and Ophiocephalus , genera characteristic 

 of the Indian region, emerge severally by a single species in West and Central 

 Africa" ; and, comparing the fishes of the Indian and African regions, he adds: 

 "A few species only have found their way into Africa." At present, the state 

 of things known thirty years ago is reversed, as twice as many species have been 

 described from Africa as from Asia. And yet, I think Gunther is right in assign- 

 ing an Indian origin to the group, for in India and Burma only do we find forms 

 (species 1 to 3) with the caudal fin quite free from the dorsal and anal, a character 

 which, as in the eels, is surely to be regarded as primitive; on the other hand, all 



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