1894.] NATITHAL SCIENCES OF PHIJ.ADELPHIA. 241 



the differentiation of the trunk line into these two groups proceeded 

 from a form at least very shuWar to pen Hsylvanica. X. penii.iijlvanica 

 resembles I{od(»ii>/s in the peculiar shape of the audital bulhc (which 

 are abruptly narrowed anteriorly), in the nearly closed spheno- pala- 

 tine vacuities, in the posterior production of the angle of the madible, 

 and in the strong inward and upward curvature of the condylar 

 ramus. It resembles Teonoma in the form of the sagittal area, which 

 is kite-shaped, narrow, sharply angular, broadest far back (on or 

 near plane of interparietal), whence its sides curve abruptly inward 

 and backward to the sides of the interparietal shield. It resembles 

 Teonoma further in the tendency to closure of the spheno-palatine 

 vacuities,^'-' the great length of the rostrum, and the presence of a 

 long trough-like depression which occupies the entire length of the 

 frontal and hinder part of the nasals. 



That the absence of the spheno-palatine vacuity is a primitive 

 character— or perhaps it would be better to say, that the presence of 

 a vacuity is a modern character — is indicated by the following facts: 

 (1 ) The ancestral genus Hodomijs has no vacuity ; (2) Xenomyx, an 

 early offshoot from the primitive Xeotomine stem, has very small 

 vacuities ; (3) Teonoma, an older type than Xeotoma proper, has the 

 vacuities closed or partly open ; (4) Xeotoma j)enni<ylva)iica, the least 

 differentiated known member of the modern genus, has the vacuities 

 partly closed ; and finally (5) some of the modernized species have 

 the vacuities closed in early life though fully open in the adult.''' 



In its geographic distribution the genus is restricted, so far as 

 known, to North America north of Dueiias, Guatemala.'* The spe- 

 cies are most numerous in Mexico and the southern United States. 

 The total number of species here recognized, including the subfossil 

 ^Y. nuu/isfc)-, is 22, in addition to which 10 subspecies are admitted. 

 It is probable that a few additional species will be added, and that 

 some of the members of the mexicana group will be reduced to sub- 

 specific rank. 



'- But there is this dittereiiee : The thin wins <»r lamella of hone whieli 

 closes or jKirtly eloses the vacuity in TcoiuDiia is derived wholly from the pala- 

 tine, wliile in X. poinsylvanica \t is made up almost equally'of palatine and 

 l)terygoi(l. In the latter species the suture between the palatine and pteryj^oid 

 moieties is on the plane of the suture i)etween the basispheuoid and presphenoid. 



'■' Allen has recently shown this to l)e the case m\Y. niicropus (Bull. Am. 

 Mus. Nat. Hi.st.. N. Y., VI, 1894, 23i»). 



'* The (iuatemala species (JS'./errii^i/wa Tomes) has not been seen by me and 

 may not be a true Neotorna. 



17 



