14 AMERICAN MUSEUM NOVITATES 
NO. 3466 

o Mes ae Pan, ge ees a 
So a es a 
= 



ey = : 
ae * eh b= 22a al © 
a —s=4. eS sl ere 
je ee 
Fig. 7. Occlusal views of right dp3 and m1 illustrating the generic difference in trigonid morphology 
of the deciduous tooth. Top, Marmosops impavidus (MUSM 13286) with a complete (tricuspid) dp3 
trigonid. Bottom, Marmosa murina (MUSM 15297) with an incomplete (bicuspid) dp3 trigonid. Note 
that whereas taxonomic variation in this trait was correctly described by Voss and Jansa (2003: character 
64), the accompanying plate (Voss and Jansa, 2003: fig. 15) was mislabeled. 
illary/premaxillary suture. The broad inter- 
orbital region is due to the considerable in- 
flation of the cranial capsule that encloses the 
olfactory bulb, behind which there is a shal- 
low postorbital constriction; the supraorbital 
margins are rounded, with only indistinct 
beading even in the largest male specimen 
examined.® The braincase is inflated and 
smooth, without conspicuous temporal scars. 
In lateral cranial view the premaxillary/max- 
illary suture is lateral to (rather than behind) 
©The terms ‘“‘bead’”’ and ‘“‘beading”’’ as traditionally 
used by systematic mammalogists to describe the dor- 
sally-grooved supraorbital ridges developed in some 
marsupials and rodents (fig. 4B) are derived by analogy 
from the upturned rims used to strengthen sheet metal 
or other flat surfaces in manufacture (i.e., the last of four 
definitions listed for the noun “‘bead”’ in Webster’s Sev- 
enth New Collegiate Dictionary, 1963). 
the alveolus of IS in most examined speci- 
mens (the suture is anterior to the alveolus 
on the left side of UMMZ 155999, and it is 
behind the alveolus on the right side of 
UMMZ 156000). The infraorbital foramen is 
very large (its anterior opening approximate- 
ly as high as P3 is tall), and the ventral de- 
flection of the zygomatic arch beneath the 
orbit is shallow. The lacrimal foramina are 
contained within the anterior orbital margin. 
The petrosal is laterally exposed through a 
fenestra between the squamosal and parietal 
bones. In ventral cranial view the incisive fo- 
ramina extend between (but not behind) the 
canine alveoli. The maxillopalatine fenestrae 
are long and narrow, extending on each side 
from a point opposite P3 to M3 or to the M3/ 
M4 commissure. The palatine fenestrae are 
