282 
When we take into account the direction of the errors, 
the results are as follows :— 
5 6° 9.” ES Don fo” CLI aaras 3) aa 
+06 + '09 + ‘05 0°0 — ‘05 - 27 — 46-51 - 85 — "93 —1'27 
Thus there is a clear tendency to over-estimate small 
numbers and to under-estimate large ones. There is an 
evident inclination towards those medium numbers which 
most frequently recurred : how far this discredits the ex 
periments I cannot undertake to say, but it is an instance 
of that inevitable bias in mental experiments against 
which it is impossible to take complete precautions. 
My conclusion that the number five is beyond the limit 
of perfect discrimination, by some persons at least, is 
strongly supported by the principles of rhythm. All the 
kinds of time employed by musicians depend upon a 
division of the bar into two or three equal parts, or into 
multiples of these. Music has, indeed, been composed 
with the bar divided into five equal parts, but no musicians 
have yet been found capable of performing it (Rees 
Cyclopedia, RuytHM). Short runs, indeed, consisting 
of five or even seven equal notes, are not unfrequently 
employed by the best musicians, but it is to be doubted 
whether the ear can grasp them surely. I presume it is 
beyond doubt that 6, 8, 9, or more equal notes in a barare 
always broken up by the hearer, if not by the performer, 
jnto periods of 2, 3, or 4. Quinary music, even if it could 
be executed, would be ill appreciated by the hearers, and, 
though all the powers of the human mind may be expected 
to progress in the course of ages, quinary rhythm belongs 
to the music of the distant future. 
W. STANLEY JEVONS 

BURMEISTER'S FAUNA ARGENTINA 
EW districts of the world are so rich in well-preserved 
remains of an extinct fauna of remarkable and interest- 
ing character as the neighbourhood of the city of Buenos 
Ayres. The immense alluvial plain of the Argentine 
Republic is the burial-place of the Megatherium, the 
Mylodon, the Glyptodon, the Macrauchenia, the Toxodon, 
and many other strange forms of ancient life, whose bones 
are ever and anon restored to light by the crumbling away 
of the soft banks of the great rivers which fiow into the 
estuary of the Plata. So abundant, indeed, are they that, 
as remarked years ago by Darwin, any line whatever 
drawn across the Pampas would probably cross the skele- 
ton of some extinct animal. 
Collections of these fossils have at various times been 
sent to several European museums, and much information 
has been published upon the nature of the animals to 
which they belonged, but these observations have been 
generally made upon imperfect or fragmentary materials. 
The fortunate circumstance of the able and energetic 
German naturalist, Dr. Hermann Burmeister, formerly 
Professor of Zoology in the University of Halle, having 
taken up his residence at Buenos Ayres, and having been 
appointed Director of the Public Museum of that city, 
has been the occasion of a systematic and elaborate eluci- 
dation of the ancient fauna of this important district. 
This has been brought about mainly by the publication 
of a richly illustrated serial quarto work, entitled “ Anales 
del Museo Publico de Buenos Aires,” the special object 
NATURE 
Oe ee 

[ Fed. 9, 1871 

sf which is to describe and figure the new or little-known 
bjects preserved in that establishment, This work, which 
vas commenced in 1864 appears at irregular intervals, but 
has already reached its sixth number, the first five of which 
constitute the first volume, thesixth, which is just published, 
being the commencement of asecond volume. Dr. Burmeis- 
er isthe soleauthor, and we havenohesitation in saying that 
it promises to be one of the most important contributions 
yet made to the knowledge of Mammalian zoology, for to 
his class is the publication mainly restricted. The parts 
ulready before us contain not only far more complete 
jescriptions and detailed figures than have hitherto been 
siven, of many of the extinct forms mentioned above, but 
it has also several admirable anatomical memoirs on rare 
or little-known living forms, especially of the Cetacea 
which occur in the estuary of the great river Plata, and in 
the adjoining part of the Atlantic Ocean, a field of re- 
search hitherto almost unexplored. 
As this work, being written in the Spanish language, is 
not so well known in this country as it deserves to be, we 
propose to lay before our readers a summary of the con- 
tents of the volume already completed, from which they 
will be able to judge of the richness and variety of the 
material which has been at the author’s disposal, and of 
the excellent use that has been made of it in his experi- 
enced hands. 
After a history of the foundation and progress of the 
public museum of Buenos Ayres, and a general essay on 
palaoatolozy, a detailed description is given of the 
skeleton of Afacrauchenia patachonica. The first dis- 
covered remains of this very remarkable animal, which is 
about the size of a camel, were found by Mr. Darwin in 
1834 at Port St. Julian on the Patagonian coast, and pre- 
sented by him to the Museum of the Royal College of 
Surgeons of London, where they are now preserved. They 
were described by Professor Owen in the appendix to the 
“ Voyage of the Beagle” (1840). Since that time butlittle 
addition was made to our knowledge of the species 
(although some bones of a smaller animal of the same 
genus, discovered by Mr. D. Forbes in Bolivian copper 
mines, have been described by Professor Huxley), until 
the lamented Bravard commenced the description, in a 
work to be entitled “ Fauna fésil del Plata,” of a com- 
paratively perfect skeleton, which was contained in the 
museum of Buenos Ayres ; but as he did not recognise its 
identity with Owen’s Macrauchenia, he gave it the name 
of Ofpisthorhinus falconerit. The premature death of 
Bravard in the earthquake which destroyed the greater 
part of the town of Mendoza, prevented the publication of 
this work ; but three of the plates, which had already been 
executed, containing figures of the skull with nearly com- 
plete dentition, and many of the vertebrae and limb bones, 
form the first three plates of the present work. To these, 
Dr. Burmeister has added another containing views of 
the pelvis and some more vertebra, and an elaborate 
description of the whole of the known bones, finally con- 
cluding that the zoological position of the genus is among 
the imparidigitate or perissodactyle Ungulata, between the 
Horse and the Tapir. 
After some remarks on the humming-birds described by 
Azara, a preliminary notice is next given on the different 
species of Glyptodon, or gigantic extinct Armadillo, in the 
museum. Three species are distinguished as well esta- 
