1898.] OF THE FAMILY MOEMTRIDiE. 777 



concurrently with the loss of the ventral and anal fins, the caudal 

 fin has been suppressed, the tail terminating in a free, irregularly 

 segmented, calcified notochordal filament. 



Although I have not at present sufficient osteological material 

 at my command to undertake a thorough study of the skeletons 

 from a systematic point of view, such characters as I have been able 

 to observe, on the skeletons of one or two species of each of the 

 genera and with the aid of the Eontgen rays, through the kind 

 assistance of Messrs. J. H. Gardiner and J. Green, show that the 

 generic definitions will be materially strengthened when the number 

 of vertebrae can be recorded ; this I have therefore now attempted, 

 perhaps somewhat prematurely, considering the comparatively 

 small number of species examined in that respect. In most of the 

 genera, the vertebral column must be divided into three principal 

 regions : — 1. The praecaudal proper ; 2. An intermediate region 

 with strongly developed ribs attached to closed haemal arches, under 

 which the posterior portion of the air-bladder extends ; 3. The 

 caudal proper. The second region does not exist in Mormyrops, 

 Isichthys, Stomatorhinns, and Gymnarchus. I have ascertained the 

 number of vertebrae in 15 species belonging to the 11 genera defined 

 below : — 



Mormyrops anguilloides 24+37=61. 



„ zancUrostris 22 + 34 = 56, 



Petrocephalus bane 9+ 4 + 29=42. 



Isichihys henryi 26 + 38=64. 



Marcitsenius discorhynchus .... 9+ 5+27^41. 



„ plagiostoma 12+ 4 + 30=46. 



„ luilvertlii 12+ 5 + 27 = 44. 



Stomatorhinus microps 14 + 25=39. 



Myomyrus macrodon 14+ 4 + 32=50. 



GnatJionemits tamandua 12+ 6 + 27=^45. 



„ rhynchophorus .... 13+ 4+30=47. 



Mormyrus Tcannume 13+ 7 + 30=50. 



Hyperopisus hebe 15+ 6 + 38 = 59. 



Genyomyrus donnyi 13+ 7+29=49. 



Gymnarchus niloticus 45 + 75 = 120. 



That the numbers vary within certain limits need hardly be 

 added, but so far little has been done in this line of investigation, 

 except by Hyrtl, who has supplied information on the following 

 species : — 



Mormyrops anguilloides 23+36=59. 



„ deticiosus (zambanenje) .. 23 + 39 = 62. 



Petrocephalus bane 9+ 6 + 27=42. 



Gnathonemus cyprinoides 13+ 8 + 27=48. 



Mormyrus caschive 12+ 7 + 30=: 49. 



„ kannume 13+10 + 31=54. 



Hyperopisus bebe 16+ 4+35 = 55. 



Gymnarchus niloticus 47+67^=114. 



These results have been utilized in drawing up the generic 

 diagnoses. 

 Pboo. Zool. Soc— 1898, No. LII. 52 



