58 
Prorer.dilu/s of the Biolo(iir(d Bonett/ of ]] ashrac/foii. 
more ocliraceous. Skull like that ol bouaneusis, but larger, with pos¬ 
terior border of palate, as iu true coijpas, sharj)ly /\-siiape [in bonari- 
e 7 isis broadly rounded eoueave, with no sharp au^le]. ll])per luolariform 
teeth increasing eonsi)icuously in size from first backward, the last with 
nearly twice the crown area of first [in coypus and bonariensis in same 
state of wear the cheek teeth are much more uniform in size], 
Mensureinents of type (from dry skin).—Head and l-)ody, 740 mm.; tail, 
415; hind foot, with claws, i;>7. Skull: (Ireatest length, 1*22.5; condylo- 
basal length, lid; zygomatic breadth, 74.0; length of nasals, 46.8; least 
interorhital breadth, dl.O; mandihle, 108.5. Teeth: Upper molar- 
premolar row, alveoli, 29.8; pin-mf 11.8; vv-m'^, IS; lower tooth row, 
alveoli, 83.9; pm-vii, 13.5; ‘20.4. 
Reniarks. —Three races of Myocaslor coypus are represented in the 
National Museum collections: coypus from Chile and Straits of Magellan, 
(Port Churruca; Ilorja Bay); bonariensis from Buenos Aires, Santa Fe, 
and Paraguay, Parana River; and santacruzx from Rio Negros and Rio 
Salado, Patagonia. 
Lagostomus maximus petilidens suhsj). mjv. 
Type from 8 miles north of Carmen de Patagones, Argentina. Adult 
[6^] skull (basal suture entirely closed); collected by Dr. Ales Tfrdlicka, 
1910. U. S. National Museum No. 172,801. 
C'/i-aracfe?-s.—-Skull (O' same essential size as in Layostomus maximns 
7naximus, hut with the incisors very much smallei-, slender and weak; 
cheek teeth averaging smaller; audital hulhe short and rounded; 
presphenoid much narrower and more tapering; opening of posterior 
nares much reduced, the post palatal space more sharply /\-shape, less 
rounded; angle of jaw much smaller, lighter and more sharply tapering. 
Measurements of type skull and teeth. — Createst length of skull, 1*26 
mm.; coudylohasal length, 117; zygomatic breadth, 75.4; length of 
nasals, 52.9; length of mandihle, to angle, 100.upi)er cheek teeth, 
alveoli, 27.2; mandibular tooth row, 27.8; total breadth of upper in¬ 
cisors at middle, 11.1 (13.8)*; depth of incisor, 5.5 (6.9). 
Remarks. —4'his form is based on a sei'ies of fifty skulls collected by 
Doctor Ilrdlicka at various points from Necochea south to Rio Negro. 
(Jompared with skulls of true Lagostomus maximus from Buenos Aires, 
San Luis, and southern Paraguay, the consi)icuously smaller, more 
slender, incisor teeth at once distinguish the southern form. 
HydrochcErus hydrochasris notialis suhs]n nov. 
Type from Paraguay. Old adult d', skin and skeleton, U. S. National 
Museum No. 154,186. Received at National Zoological Park January 6, 
I90ff, from N. Ruthn ; died .lune 25, h)09. 
* Moiisuronients in paiviitlipsos Iroin skull nf an adult mala Lagostomus maximus 
mn-ehnus from Buenos Airc's. 
