172 Dr. N. Severtzoff on the Mammals of Turkestan. 



body and the proportions of the animal's bones to each other 

 are very similar in most of the species of this genus. 



The most striking characters are those of the mane (in such 

 species as possess one) and the horns ; but whilst these are 

 only fully developed in old male specimens, the characters of 

 the skull and the marking of the skin are available in both 

 sexes and at all ages. The characters of the horns have 

 already been successfully used by Blasius for the easy and 

 exact separation of the different sheep. But in those species 

 recognized by him he has not noticed all the peculiarities of 

 the horns which are constant, and therefore may be used for 

 the more easy separation of the different species. Having 

 discovered some new species, I was consequently obliged to 

 find some new characters of the horns, which had not been 

 used by Blasius, and thus to complete the geometrical list of 

 their variations. 



The horns of an adult sheep present a double spiral. 

 1st, the inner margin of the horn describes a spiral, which 

 would fit on an inserted cone, called the axil sjnraJjyv hich. offers 

 some characteristics of which Blasius had not taken any notice. 

 2nd, round the horn-core, even if it were straight, run three 

 edges each describing one spiral along the whole length of the 

 horn-core ; this is the edge spiral^ which has been used by 

 Blasius in defining specific distinctions. 



The whole spiral of the inner margin is divided into three 

 curves: 1st, the Z)asaZ cwrue ascends; 2nd, the median curve 

 descends ; 3rd, terminal or final curve, which again ascends. 



The directions of these curves from the vertical section of 

 the skull may be represented by straight lines or chords ; the 

 angles formed by these chords and the axis of the vertical 

 section of the skull serve also as characters for distinguishing 

 the different species. Furthermore, the horns of all sheep 

 present three surfaces separated by more or less rounded edges, 

 of which latter the two exterior are the " nuchal edge " and 

 '■'•fronto-orhital edge^'' and the third the interior or '■''fronto- 

 nuchal edge.'''' Of the three sides or surfaces of the horns, the 

 two most interior may be called the ^''frontal surface " and 

 ^'■nuchal surface'''' (which meet at the fronto-nuchal edge), and 

 tJie third the exterior or ^'orbital surface.'" 



The edges, the surfaces, and the imaginary chords of the 

 horns offer very good specific distinctions. The differences in 

 the horns, as already mentioned^ are completely visible only 

 in adult male specimens ; and the younger the animals the 

 more similar are their horns. The form, the separation, and 

 articulation of the different bones of the skull are most distinctly 

 seen in young specimens — that is, as long as the separate bones 



