On the characteristic Fossils of the Chalk Formation. 381 
row subterminal black-brown band ; tail and underside of body 
white, scarcely black varied ; whiskers thick, black, white at the 
base ; upper cutting-teeth with a distinct subcentral longitudinal 
groove. 
Young. Fur ——? 
Cercolabes prehensilis, var. Waterhouse, N. H. Mamm. ii. 414. 
The skull of the Bolivian specimen is much larger, wider over 
the orbits and much higher from the palate to the nose and 
forehead than in the Brazilian specimens : the grinders are con- 
siderably smaller, and it has the peculiar groove on the upper 
grinders, but the latter may be an accidental or individual pecu- 
liarity. 
The followmg measurements in inches and lines of three 
skulls im the Museum collection will show these peculiarities. 
No. 1] is the skull of the Bolivian specimen ; No. 2 that of the 
Brazilian specimen: these animals are nearly of the same size. 
No. 3 is a skull of a skeleton from the Brazils. : 
in, lin in. lin in c 
MAL MLN GEM, CHEE Llores. tit stectucsercsecetnes 4 2 3.5 3 7k 
NVLGEN tis OFIIIE } A ow sdoai ole sick vik. Gelagay 2464 2 2 2 3 
= OVE OLDIE), eer ecacsccncisvenaents cee 2 4 Tl  Of.. Al eee 
ALANLOSC wictasie se orasoas sac acclcsaeisaces Pie wle. o. ene 0 112 
Height from palate to tip of nose... 1 5 ip eee 
——-— from palate to top of forehead. 2. 2 1 9 1410 
Of teeth Series)... 565 cseces0e 0» 98 )..0) DR. bO 10 
There is a specimen in the Museum which- Mr. Waterhouse 
has described as a variety (Hist. Mamm. ni. 415). It is very di- 
stinct in appearance from either of the above, but best agrees with 
the specimen from the Brazils in the blackness and slenderness of 
the whiskers and the smoothness of the upper cutting-teeth, and 
the blackness of the tip of the tail, but differs in the general co- 
lours being much blacker, and in the underside of the body and 
tail being nearly black and only very slightly grizzled, and espe- 
cially in the tips of some of the spines on the sides being yellow. 
I strongly suspect it will prove a third species, to which the 
name of C. tricolor might be attached. 
XXX V.—On the characteristic Fossils of the Chalk Formation. 
By L. Von Bucu*. Communicated by Prof. J. Nicot. 
TurovucHourt all the members of the chalk formation, three chief 
forms of organic beings seem especially adapted to serve as cha- 
racteristic fossils. These are the Ammonide, the Trigonie, and 
* From Betrachtungen iiber die Verbreitung und die Grenzen der Kreide- 
Bildungen. Bonn, 1849. 
