250 REV. 0. P. CAMBRIDGE ON A [May 7, 
characters as the form of the palate-ridges and the number of the 
mamme, have remained quite unaffected during all the changes that 
the rest of the animal has undergone. 
A parallel case, but one in which the differences between the two 
are by no means so strongly marked, is that of the rare Floridan 
Neofiber’, in its relationship to the common and widely-spread 
North-American Fier. 
But the question next arises as to which of the Murines Xeromys 
itself is most allied; but here the very high specialization of its 
teeth presents the same difficulty as in the case of Hydromys, so that 
in this respect the discovery of Yeromys hardly helps us at all. The 
slight differences between the teeth of the two genera prove that the 
almost continuous walls round the lobes of the molars of Hydromys 
were formerly cusps, as in other Murines; but although this leads 
directly towards Mus, it leads equally directly towards nearly all the 
other members of the family. In fact one cannot say with absolute 
certainty that the teeth are more nearly allied to those of Mus than 
to those of Uromys, Hapalotis, Gerbillus, or even Cricetus itself; 
and we must therefore be content to wait in the hope that more of 
the missing links, either fossil or recent, may yet turn up, and that 
then a more enlightened study of larger material may tend to eluc - 
date this most interesting question. In any case we must be thankful 
that by the preservation of the apparently common-looking little 
Xeromys myoides, so important an advance in our knowledge of 
the ancestry of Hydromys has been made practicable. 
EXPLANATION OF PLATE XXIX. 
Figs. 1-4. Skull of Xeromys myotdes. 
5. Palate-ridges of ditto. 
6, Anterior zygoma-root of ditto. 
7. Anterior zygoma-root of Hydromys chrysogaster. 
8,9. Ear and right hind foot of Xeromys myoides. 
10-12. Left upper and lower molars of ditto. 
2. On a new Tree Trap-door Spider from Brazil. 
By the Rev. O. P. Camarines, M.A., F.R,S., C.\M.Z.8., &e. 
[Received April 10, 1889.] 
Class ARACHNIDA. 
Order ARANEIDEA. 
Fam. THERAPHOSID, 
Gen. nov. DENDRICON. 
DENDRICON RASTRATUM, Sp.n. 
This genus is evidently nearly allied to Moggridgea, Cambr., but 
the presence on the falces of a strong rake-like group of spines near 
the base of the fang, and a difference in the form of the maxille and 
labium, lead me to conclude that it is certainly distinct from that 
1 See True, P. U.S. Nat. Mus. vii. p. 170 (1884). 
