358 



MISS JOAN B. PROCTER ON THE NUMBER OF 



nation of the lOtli series, usuall}^ takes place at about the level of 

 the 6th ventral plate — a range bearing relation to the scaling at 

 the back of the head, rather than that of the body. Since the 

 primitive number of series for the body is probably 19*, it is 

 this pair of series which wouhl develop in species haviug 21. 

 Exclnsive of this, the scale-formula is 19-17. Tlie reduction to 

 17 is brought about by the dropping out of the IVth series in 

 accordance with the laws of sequence formulated by Dr. Ruthven 

 for the Ga.rter-snakes ; which is exactly what onewonld expect, as 

 these snakes also belong to the genus Tropidonotus in the wide 

 sense. 



19-17. 



The abridged series responsible for the drop from 19 to 17 rows 



are unquestionably in course of reduction. The termination of 



the lYth series (see text-fig. 1) occurs at a point 3/5ths dowir the 



length of the body, or sometimes 5/9ths, O^casionall}^ this series 



Text-figure 1. 



Tropidonotus natrLv, lateral view, to sliow tenniiiatiou of series IV., 

 ^tlis down the Ijody. 



fuses with the Yth, this point being marked by a large scale 

 bearing two converging keels. The exact range of variation where 

 the J Vth series may be dropped, is '55 to '60 of the length of the 

 body t, which shows that there is very little individual variation, 

 and proves that the scutellation of the Cirass-snake is in a stable 

 condition. 



2. Goronella aastriaca. — On the neck this snake has 21 rows of 

 scales, the reduction to 19 usually taking place at about the level 

 of the 8th ventral by the termination of series V. or its fusion 

 with IV. 



The primitive number of scale-rows for this genus is 19. 

 Series Y., therefore, which is only present on the neck of 

 G. austriaca, becomes progressively developed in species having 

 21, or more, rows of scales. 



The complete scale-formula for 0. austriaca exclusive of the 

 neck is 19-17-15, these two pairs of abridged scale-i'ows being 

 formed by reduction. 



* Id view of the t'iict that it is the most frequent nunil)er in the genns, as well as 

 in Colubriils generally, irrespective of the affinities of the species. 



■j- " Body" iu tins paper signifies the head and trunk exclusive of the tail. 



