296 ZAGLOSSUS. 



cervical ribs are regarded as primitive. The succeeding ribs are attached by 

 their capitula only, since the tubercula are wanting and articulate by demi- 

 facets with two contiguous vertebrae. An anomalous feature in monotremes 

 is the perforation of the neural arches of the dorsal and succeeding vertebrae 

 by their spinal nerves, which usually issue from between the vertebrae in other 

 manmials. According to Gregory (1910) this seems to be a unique feature. 



The vertebral formula for the Proechidna is given by Gervais (1877-78) 

 as: — C 7, D 17, L 4, S 3, Ca 12 = 43 which is thus one dorsal and one lumbar 

 more than ordinarily assigned to the Echidna. This is the vertebral formula 

 commonly ascribed to the Proechidna, and tlie additional vertebrae are consid- 

 ered as forming an important generic character. No new observations as to 

 the vertebral formula have been pubHshed except that Dubois (1884) in urging 

 that 17 instead of IG pairs of ribs may be considered one of the generic characters, 

 adds that a skeleton examined and briefly described by him had but 16 pairs. 

 Two of the spechnens in the collection of the Museum of Comparative Zoology 

 are accompanied by nearly complete skeletons, both of which were carefully 

 cleaned by the writer; in addition the mounted skeleton belonging to the United 

 States national museum has been studied. From these various sources, the 

 following data are derived as to the vertebral formula: — 



Gervais (lS77-'78): C 7, D 17, L 4, S 3, Ca 12 = 43. 



Dubois (1884) : C - D 16, L -, S -, Ca — = — . 



M. C. Z. 12,414: C 7, D 16, L 4, S 3, Ca 12 = 42. 



M. C. Z. 12,415: C 7, D 16, L 4, S 3, Ca 11 = 41. 



U. S. N. M. 22,992: C 7, D 16, L 5, S 3, Ca 12 = 43. 



As was perhaps to have been expected there is a slight amount of varia- 

 tion. The usual seven cervicals are present in all the cases known; but in the 

 Echidna there is variation even here, for Broom (1900) has recorded a case in 

 which eight cervicals were present. Four of the five specimens have 16 dorsals 

 and the fifth has 17, so that the usual number may fairly be considered 16 as 

 in the Echidna. An additional young specimen in the collection of the Museiun 

 of Comparative Zoology, has, however, but 15 pairs of ribs. The interpretation 

 of the lumbar and sacral vertebrae appears to ha\'e offered some difficulty. In 

 the Echidna these are generally considered to be three each. Gregory (1910^ 

 p. 152) writes: — "Howes (1885, p. 89) gives 4 sacrals to Echidna and 3 to Ornitho- 

 rhynchus. In that case both genera would have 19 dorsolumbar vertebrae 

 {Proechidna 20) a number characteristic of primitive Marsupials." In Gregory's 

 opinion, however, "the anterior 'sacral' is only a slightly modified lumbar and 



