OSTEOLOGY. 



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lishment a number of years ago. The second anomalous specimen is M. C. Z. 

 7,009, collected by Dr. Thomas Barbour in Sorong, New Guinea. This specimen 

 has the usual three claws on each of the fore feet, but a small extra claw on digit 5 

 of each of its hind feet. This extra claw measures 9 mm. in length. There are 

 several other cases of variation on record, as follows: — 



Thomas (1907a, p. 499, footnote) records that the type specimen of his 

 Acanthoglossus hruijnii bartoni had five claws on both of the fore and hind feet, 

 as in the Echidna. Weber (1888) describes at length a specimen in Amsterdam, 

 that had five functional claws on both fore feet, and four on each hind foot. 

 From his figure it is seen that the supernumerary claw on the hind foot is that 

 of digit 5, though in the text, through error, it is given as of digit 1. Its length 

 is 15 mm., or less than half that of the fourth claw. Toldt (1906) mentions 

 two other abnormal specimens. The first of these is in the Museum at Brussels. 

 On digit 1 of the right fore foot is a second phalanx bearing a claw 12 mm. long. 

 The left fore foot, however, has but the usual three claws on digits 2, 3, 4, as 

 have also the hind feet. The second individual is in the Umlauff museum 

 at Hamburg. The left fore foot only of this individual is abnormal in that 

 each of the five digits bears a claw. That of digit 1 is short and rounded but 

 that of digit 5 is more fully developed, 11 mm. long and 6 mm. broad. The six 

 known abnormally clawed individuals of this genus may be tabulated as folbws, 

 the nmneral expressing the presence of a claw on its respective digit. 



Abnormally clawed Proechidnas. 



Since some twenty-five or more specimens are recorded in which the claw 

 fonnula for each foot is 0, 2, 3, 4, 0, this must be considered the normal condi- 

 tion, from which regressive variation sometimes takes place. In case of the 

 hind feet, digit 1, as might be expected from its less marked skeletal develop- 

 ment, is much more rarely clawed than is digit 5 — in fact there is but one 

 recorded case of a claw on the first hind digit. No instance is known of its 

 presence without also an accompanying claw on digit 5. No doubt the order 

 of disappearance in phylogeny is first claw 1, then 5. The reduction of the fore 



