298 ZAGLOSSUS. 



The first and second support each a smgle pair of ribs, while the third supports 

 the fifth and sixth pairs. This last piece thus evidently represents two sternebra 

 fused, as mdicated in addition, by a slight furrow on the sternebrum between 

 the last two sternal ribs, marking the point of fusion. There are four remain- 

 ing sternebra making nine in all, but these last are small and do not support 

 ribs. In an old individual the five rib-bearing sternebra are reduced to three, 

 owing to the complete fusion of the last three. Gervais's figures indicate 

 similar conditions. The dorsal end of the sixth sternal rib is greatly expanded, 

 and so likewise are the ventral segments of ribs 7 to 12, which overlap each the 

 one next anterior. Ribs 13 and 14 have a cartilaginous connection only, with 

 these bony plate-like portions, while ribs 15 and 16 are short, and backwardly 

 directed, without particular connection with the thoracic basket. 



Girdles and limbs. — The characters of the pelvic and pubic girdles are 

 in general sunilar to those of the Echidna as ably discussed by Gregory (1910, 

 p. 1.52-153). The various elements of each are in adults thoroughly fused, 

 although the line of union of the scapula with the interclavicle usually 

 remains distinct. In M. C. Z. 12,414, an old animal, the line of suture is still 

 clear between the left coracoid and procoracoid. 



There can be no doubt that the Proechidna with normally three claws on 

 each foot is a derivative from some form which hke the Echidna was five-clawed. 

 In tliis and certain other respects, it therefore represents a stage in advance of 

 the condition shown by the Echidna so that as Toldt (1905) justly says, the term 

 Proechidna is somewhat of a misnomer. Several cases are on record in which 

 more than three claws have been noted on the foot of the Proechidna, and these 

 must imdoubtedly be considered as instances of regressive variation. On both 

 fore and hind feet it is digits 2, 3, and 4 that are normally provided with claws. 

 Digits 1 and 5. are usually covered by a callosity and at most are mere promi- 

 nences in external aspect. Of the eight specimens in the collection of the Mu- 

 seum of Coinparative Zoology, two only show more than the normal three claws 

 on each foot. The first is a mounted specimen, 6,722, from northern New Guinea, 

 in which there is a claw on digit 5 measurmg about 19 mm. in both right and 

 left fore feet. I suspect that there were also claws on digit 5 of each hind foot, 

 but these if present must have become lost. The chief reason for this belief 

 is that they exist on the fifth digits of the fore and hind feet in the United States 

 national museum's specimen 22,992 which is the skeleton of apparently the 

 same individual whose mounted skin is in the Museum of Comparative Zool- 

 ogy. Both were purchased independently from Ward's Natural science estab- 



