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Show 332 MR. O. THOMAS ON THE RACES OF 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. Liitken , Dr. Collett2, 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 measurements of two extreme examples :- Second claw. Third claw. Percentage. millim. millim. Specimen s (Tasmania) 44 39 89 „ g(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, (g) 34, (a) 37, (b) 39, &c.; but, so far as regards specific 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 proportions of claws being quite as in average E. setosa. Specimen f, also from Queensland, has a third claw 33 millim. long, and 79 per cent. of the second. The two northern races E. lawesi and E. actdeata 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 digging 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 g lg85j p 14g# |