488 CTENOMYS AND PETROMYS CHAP. 
example of 120 mm. The tail too is reduced, being in the same 
example only 42 mm. in length. As in the last two genera the 
large intestine is about one half of the length of the small 
intestine. 
The “Tuco-tuco,” genus Ctenomys, has also short ears and 
tail. The claws of the fore-feet are longer than those of the 
hind-feet. 
A related form is Aconaemys (better known as Schizodon), 
with similar external characters; it inhabits high localities on 
the Andes. 
Petromys is the only genus of the sub-family which is not 
American in habitat. It is an African form and there is but one 
species. Its anatomy conforms to that of the genera already 
considered. The main difference in structure is shown by the 
teeth. Their surface is uneven, and differs from that of other 
Hystricomorphs “in that the enamel to the inside of each upper 
jaw - tooth and outside on each lower jaw- tooth forms two 
tubercles, to which correspond grooves in the reverse position of 
the applied teeth.” 
Sub-Fam. 2. Loncherinae.— The genus Achinomys with 
thirteen species belongs to the Neotropical region. The members of 
the genus are entitled “Spiny Rats” since they have spines mixed 
with the fur. The tail is long and the ears are very well developed. 
Both feet are five-toed. The tail is scaly as well as haired. 
Trichomys (also called Nelomys) is very close to the above, and is 
also from the same part of the world. 
The genus Cannabateomys contains but one species, C. 
amblyonyx, which was formerly included in the genus Dactylomys, 
but has lately been separated by Dr. Jentink.! The animal is 
Brazilian and has a total length of 520 mm., of which 320 mm. 
belong to the tail. It is a climbing rat, and in accordance with 
that way of life has undergone some modifications. The fore- 
feet are four-toed, the two middle toes being markedly longer 
than the outer ones. The hind-feet are five-toed with the same 
ereater development of the two middle toes. The claws are 
small and somewhat nail-like. 
Dactylomys, also Brazilian, and with but one species, J. 
dactylinus, differs from the last in the fact that the molars are 
simpler in form; they are divided into two lobes, each of which 
1 Notes Leyd. Mus. 1891, p. 105. 
