1896.] ZOOLOGICAL BXPHDITION TO MADAGASCAR. 979 
uromys, Hypogeomys—Brachytarsomys stands somewhat apart from 
the others and requires further investigation—belong to the so- 
called Cricetine group o: Muriform (“ Muride,” auct.) Rodents, 
of which they are the lowest of existing forms, having affinities 
with some of the least specialized of the family Dipodide, as defined 
by Winge, viz. to Sminthus and Zapus. 
The African and Asiatic Rhizomyes, usually considered as 
belonging to the Spalacide, but which the last-named author 
places amongst the lowest Muride, alongside with the tertiary 
Cricetodon and Eomys, are nearly related to the Malagasy group of 
Rodents by means of the Abyssinian Tachyoryctes (Rhizomys) and 
the Malagasy Brachyuromys, the former being but a very specialized 
fossorial form of the more generalized Brachyuromys ramirohitra. 
The molars are almost identical in botb, only but slightly more 
hypselodont in Tachyoryctes. If we divest the Tachyoryctes skull 
of its fossorial characters and of the consequences of the more 
hypselodont molars, we obtain a Brachyuromys skull. Likewise 
the skulls of the young Tuchyoryctes bear much greater resemblance 
to Brachyuromys than the adult. There is further a great corre- 
spondence in external characters if we disregard the smaller ears 
and eyes of Yachyoryctes and its fossorial claws. 
As to the affinities of the Malagasy Rodents with the lower 
Dipodidee, they are revealed by the skull as well as by the confor- 
mation of the molars. The infraorbital foramen is large through- 
out and especially in Brachyuromys, though on the whole showing 
the form characteristic for the Muride', the posterior part of 
the zygomatic arch is bent downwards, the malar bone strongly 
developed and approaching the lachrymal more than in any other 
Muridz, the size and shape of the incisive foramina nearly approach- 
ing what obtains in the Dipodide, &. With regard to the teeth, 
the group of Malagasy Rodents, together with the Abyssinian 
Tachyoryctes, differ in a very important condition from the more 
specialized Murine, and even from the Cricetine Rodents, in 
having their molars of almost equal size and form; the two 
anterior molars especially are very much like each other. This 
likewise is a character in which they approach the lower Rodents, 
especially the Dipodide; in the pattern of the molars there is 
equally a strong resemblance of them all with Dipodide (Sminthus, 
Alactaga, Zapus); in this respect the mosaic pavement-like tri- 
turating surface, both in the Malagasy Gymnuromys and the 
Nearctic Zapus, is especially noteworthy. 
The relation of the Madagascar Rodeuts to Cricetus, which is 
considered to be the type of the group, is viewed by me as 
1 The miocene Paciculus, from the John-Day beds in N. America, is con- 
sidered by Scott to stand in most respects in an intermediate position between 
Protoptychus (which Scott supposes to be the ancestral form of the Dipodide) 
and the Dipodidz, although it has lost all the premolars, and the lower portion 
of the infraorbital foramen forms, as in the Muride, a distinct notch for the 
passage of the nerve. (‘ Protoptychus hatcheri, a new Rodent from the Uinta 
Eocene,” Pros. Ac. Nat. Sc. Philadelphia, 1895, p. 269.) 
