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 
mammals. According to Gregory (1910) this seems to be a unique feature. 
The vertebral formula for the Proechidna is given by Gervais (1877-78) 
as:— C7, D17, L 4,83, 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 the additional vertebrae are consid- 
ered as forming an important generic character. No new observations as to 
the vertebral formula have been published except that Dubois (1884) in urging 
that 17 instead of 16 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 specimens 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 (187778): C7,D17, L 4,83, Cal2 = 43 
Dubois (1884): C-,D 16, L-,8-, Ca— = —. 
M. C. %.12,414:°  ©7, D164, 83, Cal2 = 42. 
M.C.Z. 12,415:  ©7,D16,L4,S83, Call = 41. 
U.S. N. M. 22,992: C7, D 16, L5, 83, 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 Museum 
of Comparative Zoélogy, has, however, but 15 pairs of ribs. The interpretation 
of the lumbar and sacral vertebrae appears to have 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 
(Proéchidna 20) a number characteristic of primitive Marsupials.”” In Gregory’s 
opinion, however, ‘‘the anterior ‘sacral’ is only a slightly modified lumbar and 
