332 MR. O. THOMAS ON THE RACES OK ECHIDNA. [Apr. 21 



development of the hairs and spines and the comparative amounts of 

 brown and white on' the latter ; but the only strictly geographical 

 variation in colour that I can distinguish, is that southern specimens 

 have a general tendency to have the crown of the head a lighter brown 

 than the back, the converse being the case in northern ones. This 

 is, however, by no means invariable. 



The next thing to be considered is the relative lengths of the hind 

 claws, on which great stress has been laid by Dr. Lutken\ Dr. 

 Collett^ and others, and indeed the differences in this respect are 

 very remarkable, and might easily be taken to represent specific 

 distinction. The extreme forms are represented by figs. C and D on 

 Plate XXIV., and it will thus be seen that in one form (C) the third 

 claw is nearly as long and as stout as the second, and about twice the 

 size of the fourth ; while in the other form (D) the third is scarcely 

 bigger than the fourth, and not more than from one third to one half 

 as large and as strong as the second. The following are the mea- 

 surements of two extreme examples : — 



Second claw. Third claw. Percentage. 

 milHm. ruillim. 



Specimen s (Tasmania) 44 39 89 



„ ^(N. S. W.) 39 14 34 



This character runs for the most part parallel with geographical 

 distribution, the southern forms having in a general way the long 

 third claws, and the northern the short ones : thus 13 typically 

 hairy specimens of var. setosa have percentages ranging from 70 to 

 100; while the percentages of northern specimens are: — {e) 32, 

 (5')34, (a) 37, {b) 39, &c. ; but, so far as regards speciiic distinction 

 based on this character, we find that certain individual specimens 

 entirely upset the general rule. Thus specimen /, very spiny and 

 obviously from the north, has a third claw 28 millim. long, and 

 bearing a percentage to the second of 80, the general size and pro- 

 portions of claws being quite as in average E. setosa. Specimen/, also 

 from Queensland, has a third claw 33 millim. long, and 79 per cent, 

 of tlie second. Tiie two northern races E. lawesi and E. acnleata 

 are absolutely indistinguishable from each other by this character. 



The reason for the greater length of the third claw in var. setosa 

 is not very evident ; but it may be that the heavier and richer soil of 

 Tasmania requires a more powerful diiiging organ for its removal, and 

 that by the increase of the length of the third claw this extra power 

 is gained, for it is obvious that in the races with short third claws, 

 the long second one does practically all the work, the third being 

 almost functionless. But by the enlargement of the latter to a nearly 

 equal length with the second, extra power is gained by both claws 

 working side by side, and thus making a broader and stronger digging 

 organ. 



Passing now to the characters of the skull, more important and 

 more interesting than any external characters can be, we must first 

 study the influence that age and sex have upon its form and size, 



1 P. Z. S. 1884, p. 150. = P. Z. S. 1885, p. 148. 



