ALLEN, EXTINCT OGTODONT FROM PORTO RICO 19 



Isolobodon* portoricensis gen. et sp. nov. 



Type, No. 38409a, from the Cuerva de la Seiba, near Utuado, Porto Rico; 

 coll. Dr. Franz Boas. The type skull has the nasals and entire upper dentition 

 complete, but lacks part of one zygoma and the braincase posterior to the 

 fronto-parietal suture. 



Desceiptiotst 



Skull. — The skull (Plate I, Figs. 3-8) closely resembles in outline and 

 proportions that of Plagiodontia, being shorter and broader than the skull 

 of Gapromys. The most nearly complete skull of the series (ISTo. 38409&), 

 which lacks only the nasals, the occipital region and most of the teeth, 

 when laid over F. Cuvier's outline figure of the skull of Plagiodontia^ is 

 found to be essentially of the same size and form. The lower jaw is of 

 the same size, but differs somewhat in tlie form of the condylar portion, 

 which, however, is not well shown in CJuvier's plate. The nasals are of 

 nearly uniform breadth from base to tip, widening only slightly and 

 uniformly from the base anteriorly. 



The most nearly complete skull of the series is above the average in 

 size, and is also evidently tlie skull of a very old individual. This skull 

 affords the following measurements : front border of premaxillaries to 

 occipital suture, 73 mm. ; length of f rontals on midline, 28 ; length of 

 parietals on midline, 25 ; lengtb of rostrum, 25 ; width of rostrum at 

 anterior root of zygomata, 13; depth of rostrum at same point, 19; inter- 

 orbital breadth, 23.4; zygomatic breadth, 4-8.5; greatest breadth of brain- 

 case (at posterior base of zygomata), 24; palatal length, 33.5; breadth of 

 palate between premolars, 3 ; breadth of palate between last molars, 7, the 

 toothrows being strongly convergent.* The type skull, fully adult but 

 smaller and evidently younger than No. 3840 9 &^ furnishes the following: 

 Interorbital breadth, 22; length of f rontals on midline, 25; length of 

 nasals, 25 ; breadth of nasals at ])ase, 8.2 ; breadth of nasals near front 

 border, 9; length of maxillary tootlirow (crown surface), 16.5; palatal 

 length, 33.5; palatal Ijreadth between premolars, 2.5; palatal breadth 

 between last molars, 7.5 ; greatest breadth of skull (behind base of 

 zygomata), 26. 



The size of the lower jaw (Plate I, Figs. 1-2; Plate II, Figs. 1-4, 8-9) 

 varies greatly in different specimens, apparently due mainly to age but 

 perhaps partly to sex. Adult mandibular rami vary in total length (base 

 of incisor to tip of angular process), from about 48 to 56 mm.; depth at 



' i^tros, equal ; Xo/36s, lobe; bdulv - odovs tooth. In allusion to the equal lobes of the 

 molar teeth. 



♦Ann. des Sci. Nat., ser. 2, VI, 1836, pi. 17, fig. 3. 



