202 ANNALS NEW YORK ACADEMY OF SCIENCES 



Secon"d ISTew Genus of Hysteicomorph 



From a layer evidently higher than that Avhich preserved Elasmo- 

 donfomijs came the skull and mandible of a smaller hystricomorph which 

 proves equally as interesting as its larger tomb fellow and is, like it, 

 apparently unknown to science. As it presents characters widely differ- 

 ent from the hystricomorphs of the Antilles and the mainland of Central 

 and South America, I propose for it the folloAving name : 



Heteropsomys ' insulans gen. et sp. nov. 



Type. No. 14172, Dept. Vert. Pal., from Cueva de la Ceiba, near Utuado, 

 Porto Rico, 1915; collector, Dr. Franz Boas. The type skull is a partially 

 complete cranium lacking tlie nasals, the left zygomatic arch and the left 

 auditory region, but with one incisor and the first two molars in each row and 

 the right mandible with four teeth, the incisor and three molars. 



DESCRIPTION 



Skull (Plate XI, Pigs. 2-3: Plate XII, Figs. 1-5).— The skull has the 

 superior outline slightly curved from nasals to parietals, abruptly curved 

 do"waiward in occipital region. From the opening between the-premaxil- 

 laries it may be seen that the nasals are narrow posteriorly, widening 

 noticeably anteriorly. The frontals carry a peg-like postorbital process. 

 There is a short, shallow, sagittal crest along the downward-bent portion 

 of the cranium. Fairly large anteorbital fenestra are present and the 

 zygomatic process of the maxillar}^ is broad and shelf -like. The jugal is 

 heavv and wide, especially posteriorly, where it bears a prominent process 

 continued posteriorly from the lower margin of the jugal. There is also 

 a low postorbital projection at the suture of the jugal with th squamosal. 

 A shallow excavation, surrounded by a border raised from the surface of 

 the palate, is present partly in the premaxillaries, partly in the maxil- 

 laries, and contains the small incisive foramina at its anterior end. The 

 foramina are not median but are widely separated. The interpterygoid 

 fossa is carried forward into the palatines almost as far as the anterior 

 border of the third tooth of the molar series, thus forming a very exten- 

 sive V-shaped post-palatal notch. The bullse are of moderate size, evenly 

 rounded but slightly compressed laterally. Short parapophyses are borne 

 by the exoccipitals. The foramen magnum is very large proportionally. 



The mandible is very similar in shape to that of Prcechimys. The 

 coronoid is low and narrow, there is a broad shelf-like masseteric ridge 



"'Heteropsomys: erepos, different; oi/', aspect; ixvs, mouse — i. e., mouse of a difiEerent 

 aspect. 



