ffo» 1532, 
NOTES OX MALA YAX PQRCt r PJXES—LYON. 
585 
in many respects like that of Tkecurus, but relatively narrower and 
with less abrupt rostrum, and with a well marked fossa on side of 
mandible beneath the eondylo-coronoid notch and with rooted molars. 
Differs from the skull of Tricky* in the absence of postorbital pro¬ 
cesses, and in having distinctly heavier nmlars. 
EHemnl characters . — Size small, a little less that of Thteurm^ tail 
long, about one third head and body. Entire upper parts and sides 
of body and base of tail covered with heavy, somewhat flattened 
spines, with a large groove on their dorsal aspect, and a shallow 
groove on their underside at the base. The spines are longest on the 
lower back, rump, and base of tail where they are about 75 mm* long. 
No quills proper are found on this porcupine, but interspersed among 
the flattened, grooved spines on the lower back are a few rounded 
stiff bristles, somewhat quill like at the hose, having a length of 100 
to 125 mm. The head, underparts, and the legs, are clothed with soft, 
tbit spines. The basal fourth of the tail is covered with spines, like 
those of the lower back; the middle two-fourths are covered with 
scales, each of which is subtended by three short hail's, a median stiff, 
long one, with a shorter finer one on either side; the terminal fourth 
of the tail is mainly covered with peculiar flattened hollow hairs ami 
some ordinary bristles. Each of these peculiar hairs begins with a 
hair-like base, but soon expands into a small, narrow, hollow, flat¬ 
tened capsule, followed by a short hair-like space and then another 
flat, hollow capsule, some hairs having as many as five such expansions. 
These hairs always terminate in an expansion with a long drawn-out 
apex. (Plate LYII, fig, 3.) 
Skeleton . — The main features of the skull of the genus Atherarm 
have previously been pointed out. The relative size and shape of the 
skull and of its various parts are clearly shown in fig. 2, Plates LIV, 
LY, and LVI, so that no detailed description is here necessary. The 
vertebral formula is Cv, 7, D. 1-1, L. 5, S. 3, Gd. 24. The axis bears 
a large neural spine flattened from side to side, similar to that found in 
Amntkion, but subtriangular in outline and directed back ward at a 
sharper angle. (Plate LV1I, tig. 7.) The seventh cervical has a short 
neural spine, like that of the sixth, and the long spine of the seventh 
seen in Aeanthion has been shifted backward to the first* dorsal, as 
in Theeurits. The lumbar vertebra? have rather narrow lateral pro¬ 
cesses, directed forward at a more acute angle than they are in the two 
preceding genera, and the ends of the processes are somewhat enlarged. 
(Plate LYII, fig. 8.) Only three vertebra; compose the sacrum in 
Atherurm q and the first alone serves for the attachment of the ilia. 
The prestermun is relatively short, and its expanded portion rela¬ 
tively narrow. The humerus is relatively more slender in Atkerurwt 
than it is in Aeanthion or Tketmrm; the deltoid ridge is less promi- 
