Thomas, Oldfield

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218  Mr. O.  Thomas on an  instance of the theory of "repulsion J'  (described  P. Z. S. 1894, p. 144), by which when tW? allied species live together in  the  same  place,  and  can  gam  no advantage  by mutual resemblance  (" mimicry"), they often  intensify their  colour differences  to  the greatest  possible extent, in order probably that their members  shall be enabled to distinguish comrades from l'ivals as readily as possible. X,X.-Descr£pt£ons ~f  Four new Soztth-American Mammals. By OLDFIELD THOMAS. Oxymyctel'Us lano8us, sp. n. General appearance  exceedingly like  that of Akodon wan· tllOrhinus, Waterh.  Fur very  soft,  thick,  and  woolly, the wool  hairs  about 9 millim. long on  the back, and the longer straight hairs  forming  a  thick  fringe 5  01' 6 millim. beyond the wool hail's.  General colour deep yellowish olive all over above, the  sides  brighter  yellow along the junction with the belly •  Under surface slaty grey, the tips of  the hairs  buffy white.  Ears small, not prqjecting above the fur, well haired. Upper surface of hands and  feet  shining white;  pollex with a blunt  claw, hardly long  enough  to  be  called a true claw, but longer and more  compressed than a "nail."  Fifth hind toe reaching to  the middle of the basal  phalanx of the fourth. Tail about as long as  the body without the head, well haired, blackish  brown  above,  yellowish  white  below  and  on  the sides. Skull  with  a  narrow  slender  muzzle  and  a  very large rounded brain-case.  Nasals  narrow, pointed, COllCM'"e  above when viewed in profile.  Interorbital region  broad, smoothly rounded, convex  above, without  ridges.  Brain-case  broad, flattened,  rounded.  Interparietal small.  Anterior zygoma-root very narrow, slanted forwards.  Anterior palatine  fora-mina reaching  back  one third of  the  length  of  m1;  hinder edge of palate opposite back of mS.  .  . Incisors  narrow,  slender,  very  pale  yellow  above  and white below.  Molars as usual. Dimensions of the type, in skin, male:,-Head and body (c.) 80 millim.;  tail 51; hind foot  (moist,. ened)  20'6. Skull: basilal' length 18'4, greatest breadth (across brain-case)  12'.4;  nasals  9'3  X  2'8;  interorbital  breadth  4'8; palate.  length  from  henselion  9'9;  diastema  6'1;  palatal fOl'amma 5'3 X 2 ;  length of upper molar series 4. Hab.  Monteith Bay, Straits of Magellan. Tyr'  ~.M.  80.7.28.11.  Collected and presented by Dr. R. W. OopPlllger, of H.M.S. ' Alert.' Four new  South-Amer£can Mammals.  2 t9 The skin  on which  this  species  is  founded  is  that men-tioned  under  "Hespel'omys (Habl'othr£OJ)  xantllOrMnus"  in my account  of the  'Alert' collections  (P.Z.S.1881, p. 5). That determination was  based  mainly on the spirit-specimen referred  to  at  the  same  time, which  is  undoubtedly  a  true Alcodon (=  Habrothr£x).  A  comparison  of  the skulls  now shows not only that  the  two, like as  they are externally, are different as  species, but  that  the Monteith Bay skin belongs to  the  Oxymycterus  group,  as  is  especially  shown  by its narrow  slanting  zygoma-root,  slender  muzzle,  and  broad brain·case.  In that group no species  as  yet described bears any resemblance to it. Dasyprocta KaHnowskii, sp. n. Size rather large.  Fur ringed  with  black  and yellowish rufous, the  elongated  hairs  of  the  rump  white  with  black tips, contrasting  markedly with the  rest of  the body.  Area round the root of  tail black, abruptly defined from the white crest-hairs.  Under surface  yellowish,  grizzled  with brown. Feet blackish.  Tail about  an inch in length, naked. Skull  elongate, not  unlike  that of D.  variegata and  foli-ginosa, but with the muzzle rather broader and more tl'Umpet. shaped. Dimensions of the type, an adult male :-Head  and  body  (measured in flesh  by  collector)  6'30 millim.;  hind foot  125. Skull:  basilar  length  89,  greatest  breadth  54;  nasals 46 X 22;  interorbital  breadth  33'5;  diastema  30;  upper molal'  series 20'5. Hab.  ldma,  Valley  of  Santa  Ana,  Ouzco,  Peru.  Alt. 4600 ft.  0011.  J. Kalinowski, Nov. 2,  1894.  . '1'his  handsome  Aguti may be  readily distinguished  from any species  hitherto  described  by the  peculiar  coloration of its long rump-hail's,  which,  white with  black  tips, are  quite unlike those of any other species. It was  obtained  by,  and is  numed  in  honour  of,  Mr. J. Kalinowski,  the  well-known  Polish  collector,  to  whom science  is  already  indebted  for  the  discovery  of  so  many interesting Peruvian mammals. Peramys adustlts, sp. n. Size small.  Fur close and short, only about 4 millim. long on the back.  Colour all  over above uniform  finely  grizzled brown, with a slight yellowish tinge; tip of muzzle blackish. Under surface  coloured  about  as  in Mus  mltsculus; line of demarcation  on  sides  little  marked.  Ears very short, prac-tically naked.  Hands and  feet  greyish brown, digits naked. Tailpl'actically naked, its few  £ne hairs black. 220  On  Four new  South-American Mammals. Skull low and  flattened.  Nasals  much  expanded behind. Posterior  lower  premolar  slightly  smaller  than  the  middle one. Dimensions of the type, in skin :-Head and  body  100 millim. ;  tail 53; hind  foot  (moist-ened)  15; ear  (above head)  (c.)  3. Skull:  basal length (c.)  25; nasals 12'5 X 4-5; interorbital breadth 6; breadth of brain-case 11; palate length 19; com-bined  length  of  m'-S  5'1.  Lower  jaw,  condyle  to  tip  of incisors 20'5; front of canine to  back of m4 12. Hab.  W. Cundinamarca, in the low-lying hot regions~ Type.  B.M.97.7.2.1. This species has  most  resemblance in  colour to P.  domes-ticus,  VVagn.,  but  differs  by  its  much  smaller  size  and smaller ears.  From  the  known  species of  its own size it is readily distinguishable by its uniform brownish coloration. Icltthyomys trichotis, sp. n. Size  smaller  than  in  the  other  species.  Colour  dark smoky or slaty grey all  over  above  and below, with the ex-ception of  the chest  and centre  line of  the belly, which are white.  Ears  short  and  narrow, their  conch  only standing up about 4 millim. above the crown, thickly clothed with hairs similar in colour and texture  to  those on the head, and of an equal length to that of the conch itself;  as a result  the ears are  quite  lost  among  the  general  fur of  the  head.  Upper surface of hands silvery white, of feet rather more bro.wnish ; hind toes apparently rather  less  broadly webbed than in  the other  species,  and  the  pads  smaller  and  more  distinctly defined.  Tail about  as  long  as  the body without the head, , well haired, blackish  throughout  except  at  the extreme tip, which, as in 1. bydrobates and Sodm'stromi, is white. Skull  unfortunately  too  much  broken  in the  only speci-men  to  be  described,  and  it can  only  be  noted  that  the incisors,  both  above  and  below,  are  much  thinner  and nal'l'owel'  transversely  and  antero-posteriol'ly,  and  that the molars are of  about  the  same  size  and proportions as  those of 1.  hydrobates, or mS may be a little smaller. Dimensions of the type, in skin :-Head  and  body 130  millim.;  tail  114; hind  foot  28'5; ear, above head, 4. Skull: length of  upper  molar  series  4'8, of lower  molar series 4'9.  Lower jaw, bone only, 13'5; to incisor tip 16'3. Hab.  W. Cundinamarca,  in  low country near  to  Magda-lena R. Type.  B.M. 97.7.2.2. This species resembles 1. hyd1'obates, and, if really different, , On  the  Anatomy of  Apera Burnupi, E. A. Smith.  221 L  Soderstromi, in the colour of  its tail, but  differs both from these and L  Stolzmanni by the extreme hairiness of  its  ears, the restriction of  the white of  the under surface  to  the chest and centre of belly, and by the slenderness of its incisors. X:XI.-On  the  Anatomy  of Apera  BUl'llupi,  E.  A. Smith. By  W  ALTER  E.  COLLINGE,  F.Z.S.,  Assistant  Lecturer and  Demonstrator iu Zoology and  Comparative Anatomy, Mason University College, Birmingham. [Plate V.] THE  genus  of  slugs  known  as  Apera  was  originally  con~ stituted  by  Binney  (2)  in  1879  under  the  term  Ohlamy~ depkorus.  Heynemann  (6),  however,  suggested  the  term .Apem,  on  the  ground  that Binney's name indicated  a  false characteristic,  viz.  the  presence  of  a  mantle-lobe.  Later, Mr.  Edgar A.  Smith  (8)  pointed out that Agassiz  (1)  had employed  the term Ohlarnydopkm'us,  which is  practically the same  as  that used  by Binney,  for  a  group of  mammals,  a fact which Heynemann does not seem  to  have been  aware of. There  are  only two  known  species of this genus, namely, A. Gibbonsi, W. G. Binney, from Natal (2), and A. Burnupz", E. A. Smith, from  Natal (8).  . 1\1y  best thanks  are  due  to  M.  Edgar A. Smith, forhi8 kindness in supplying me with the material upon which these observations on the anatomy have been made. The  specimen  from  which  all  the  figures  were  drawn measured  49  millim.  in  length.  . It cOl'l'esponded  in  all external features to the original  description  (H).  Mr.  Edgar A. Smith has pointed out that the carinre are doubtless much accentuated in alcoholic specimens; this I can confirm, for  on being  immersed  in very  weak alcohol  they  were much  less conspicuous, the dorsum being more convex.  Mr. Smith has since. sent  me  a  note of some observations he made  upon  a living  example,  in which he  points  out  that the  keels  are visible  but  less  acute  than  in  the  contracted  state.  In Heynemann's  figures  (6, T.  2.  figs.  5  & 6)  of A. Gibbonsi the  keel  which  limits  the back  is  not  shown.  This same author (6, p. 19), although only acquainted with the external features  of  A.  G£bbonsz',  suggested  that the  genus  Apera belonged  to  the Testacellidre;  on  p.  19 he  writes ~-" Dann springt uns sofort die nahe Verwandtschaft  mit Testacella  in die A  ugen,  die  gemeinsame allgemeine Gestalt (s.  Fig.  von Gibbons),  die  gemeinsame  Lage  del'  Gel1ital-, Athem- und Afteroffnung,  die  ahnliche  strahlige  Ronl1elung  urn  diese Korperoffnung  hel'um,  die  iihnliche  Runzelul1g  libel'  die Liinge  des  lWckens  (s.  Figur  van  Gibbons  und  seine 

Descriptions of four new South-American mammals

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