1911.] F.H.Stewart: Cyprinidae from Tibet. 79 



but their eyes are actually of the same average size (4" 75) ^s the 

 average of groups P. 2 and 3 (4" 75), and are considerabl}' smaller 

 than the average of the other two Ssewerzoff groups P. r and 

 4 (4'30) {vide table i, cols. 4 and 5, Ch.). 



Character (c) {vide pi, iii, figs, i, 2 and 3). Herzenstein states 

 that in 5. sever zovi the anterior end of the mouth-cleft is on a 

 level with the inferior margin of the orbit, and that in S. stoliczkae 

 it is below this level. 



Alcock considers that this difference is due to the greater rela- 

 tive size of the eye in the former species. After examining the 

 new collections from Tibet the present writer cannot agree with 

 the view that this character is entirely dependent on the size of 

 the eye. The heads of the two extreme types, Ssewerzoff 's and 

 Stoliczka's, differ in the following points : — 



Stoliczka's (pi. iii, fig. 3)^ — 



{a) the lower surface of the head from the tip of the snout 

 back to the pericardial region is almost perfectly flat ; 



{b) the mouth, which opens on this flat surface some few 

 millimetres from the tip of the snout, is entirely ven- 

 tral ; 



ic) since the tip of the snout lies in the lowest horizontal 

 level, the angle formed by the frontal line curving from 

 the snout to the occiput with the horizontal is greater 

 than if the tip of the snout were in a higher level. 



Ssewerzoff's (pi. iii, figs, i and 2) — 



{a) the lower surface of the head is curved, rising from the 



pericardium to the tip of the snout; 

 (6) the mouth is thus more terminal than ventral and is 



onl}' slightly overhung by the tip of the snout ; 

 (c) the snout being in a higher level the angle referred to is 



less than in Stoliczka's type. 



Gradations between these two extremes occur. Stoliczka's 

 type is more common than Ssewerzoff's. 



The Ssewerzoft" type of head occurs in groups P. i (Herz.) and 

 Ch., and in half the specimens of P. 4; in the other half the heads 

 incline more to Stoliczka's type as here defined. 



Character {d) , colour. There is no type of coloration abso- 

 lutely characteristic of either the Stoliczka or Ssewerzoff head 

 types. Spotted and uniformly coloured forms occur in both but 

 the former is more generally uniform in colour, the latter spotted. 



Character {e), smaller size of sexually ripe specimens of 

 S. severzovi. In group D. 2, with the Stoliczka head type, the 

 reproductive organs are at least as well developed as in P. 4, 

 although the average length is 123 mm. in the former as compared 

 with 145 mm. in the latter. 



The two species, then, cannot be separated by all five charac- 

 ters, since different combinations occur in each group. 



