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Show Y OF THE VOYAGE OF TilE BEAGLE. l06 ZOOLOG . . . the am.m a1 to t h e c d but to brino- the food w1thm tOO ' o not, as in the Sloth~, to cmry rootin the trees on which it grew. the reach of the ammal, by up ~ . 1 'dence of the frame-work of a . f tl M athermm we lave evi In the remams o le eg . . d llawling down the largest mem- 1 tl t 'k of undermmmg an . lluadrllped equa to le as t. 011 1·t 1·s obvious that the imme(hate . 1 c t I the latter opera 1 b rs of a trop1ca 10res ·. 11 • • th trunk of the tree would demand a . . f th t . or extrem1t1eS to e applicatiOn o e an eti 1 d 't ·s the necessity for an adequate d. f 1 n to be effectua , an 1 1 .. correspon mg u crm ' . , ch an a plication of the forc-extrcm1t1es basis of support and re~Istance to su d:velo Jment of the pelvis, tail, and which gives the explanation to the ~n~malo~s· d I No wonder therefore, that hinder extremities in th.c Megathe~·w•~ (~a ~upe sl~all we now ftnd quadrupeds their type of structure IS so peculiar, or w lC~e s . . 1 equal, like them, to the habitual task of uprootmg trees for food . DESCRIPTION OF FRAGMENTS OF BONES, A ND OF. OSSEOUS TESSELATED DEitMAL J ' , COVEIUNG OF LAlWE EDEN TATA. It is now determined that there once existed in Sou~h A1~erica, besid~s the Me-tl : m the Megalonyx, anu the allied genera descnbed m the precedmg pages ga lenu ' B b 1 · to the Anna-of the present work, gigantic species of the order ntta e o~gmg. . 1'11 f· ·1 arld defended like the small existing representatives of that fam1ly, C I 0 J.l1ll y, < ' • f l by a tesselated bony dermal covering. The larg.est known spec1es o ~ 1ese ex tinct Dasypodidce is the G l!Jplodon clavipes, of ~h1ch the ~nnour .and pm ts. ~f tltc skeleton have been described by MM. We1 s and DAlton m the Berltn Transactions for 1827 and Hl34 : and the generic and specific characters and name, with an account of the dental system, and bones of the extremities, were recorded in the Geological Proceedings for M.:Hch 1839. It would seem that parts of the same, or a nearly allied gigantic species 'Nere described in the ~a me year by M. Lund; under the name of Iloploplwrus. Of the valuable and .wtercstinc,. discoveries of this able Naturalist I regret that I was not aware until the appea~·ance of a notice of them in the Comptes Rendus for April, .1839.* Amongst the fragments of bony tesselated armour in Mr. Darwin's collectiOn are a few pieces whi •h were found by him, associated with remains of Toxodm~ and Glossotherinm near tlte Rio Negro in Banda Oriental. ·!· These fragments, 1f we m:ty judge from their thickness, must have belonged to an animal at least us * An excellent translation of the description of the Brazilian fossils found by l\1. Lund, is published in tho Annals of Naturalllistory, July and August, 1839. t At the distance of a fow leagues from the locality hero mentioned, other fragments were founu by Mr. nan,·in; al:o ncar Santa Fe, in Entre Rios; also on the shores of tho Laguna, ncar tho Guardia del Monte, ' 'onth of BLtcnos Ayres; also, according to the Jesuit Falkner, on tlte ba.uks of the Tercero. FOSSIL MAMMALIA. 107 large as the Glyptodon clavipes; but the pattern differs in the greater equality of size of the component tesserre. The thickness of the largest fragment is one inch and a half, the tesscrre vary in diameter from one inch to half an inch, and are separated by grooves about two lines in depth, and two in diameter. The pattern formed by the anastomosis of these grooves is an irregular net-work; the contour of the tesserre is either unevenly subcircular, hexagonal, pentagonal, or even four-sided ; with the sides more or less unequal. In those portions of this armour, where one of the tesseroo exceeds the contiguous ones in size, the imagination may readily conceive it to be the centre of a rosette, urounu which the smaller ones arrange themselves, but there is no regular system of rosettes, as in the portions of the dermal armour of the Glyptodon figured by ·weiss, and those brought to England by Sir Woodbine Parish, in which the central piece is double the size of the marginal ones. The portions of the tesselated bony dermalcoveringof a Dasypodoid quadruped, figured in Pl. XXXII. figs. 5 and 4, of the natural size, were discovered folded round the middle and ungueal phalanges, figs. 2 and 3, at Punta Alta, in Bahia Blanca, in an earthy bed interstratified with the conglomerate containing the remains of the fossil Edentals. In one of these fragments, measuring six inches long by five broad, the tcsserre are arranged in rosettes, and so closely correspond in size and pattern with the bony armour described by M. Lund, as characterizing his species, IIoploplwnts eupltractus, that I feel no hesitation in referring them to that animal. One of the pattern rosettes is figured at fig. 4, togethe1· with the thickness of the armour at this part, and the coarse tubulo-cellular structure of tl1e bone. Another portion of dermal armour from the same locality, gives the pattern shown in fig. 5, formed by square or pentagonal tesserre, arranged in transverse rows; it is certaiu that this portion of armour belonged to the same animal as the preceding piece; and probably that it constituted part of the transverse dorsal bands of the Ifoplopltorus. The middle and ungueal phalanx, as well us the portions of armour, are given of the natural size, in Pl. XXXII. The upper and outer surface of the phalanx, is shown in fig. 2. It is smooth and flat ;joins the inner surface by a sharp euge, which runs along the upper and inner side of the bone; and passes by a gradual convexity to the under surface; the ridge correspondiug with the base of the claw, is feebly developed at the under and lateral parts of the base of the claw. Below the double trochlear joint fo•· the middle phalan~, there arc two articular surfaces for two large sesamoid bones. The middle phalanx corresponds in its small antero-posterior diameter and wedge-shape, with that of the great Glyptodon: but the terminal phalanx is longer and deeper, in proportion to its breadth. P2 |
