OCR Text |
Show 250 REV. O. P. CAMBRIDGE ON A [May 7, characters as the form of the palate-ridges and the number of the mammae, 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 Fiber. 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 Xeromys 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 myoides. 5. Palate-ridges of ditto. 6. Anterior zygoma-root of ditto. 7. Anterior zygama-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. CAMBRIDGE, M.A., F.R.S., C.M.Z.S., &c. [Eeceived April 10, 1889.] Class ARACHNIDA. Order A R A N E I D E A . Fam. THERAPHOSIDJE. 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 maxillae 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). |