26 VARIATION, DISTRIBUTION, AND EVOLUTION OF THE GENUS PARTULA. 
yellow brown. A parietal tooth is entirely lacking. The foregoing diagnosis is 
rendered more concrete and precise by the illustrations (figs. 1to 11, plate 11) and the 
tables (tables 5 to 8). Habitat: thick vegetation below the summit of Mount 
Salifan, Guam; altitude, 700 to 800 feet. 
In the nature of the case, the locality where the new species was found is 
especially noteworthy. Mount Salifan is reported on the charts as over 800 feet 
in height, and it constitutes the northernmost member of the middle section of the 
mountain range in the western half of Guam. The highlands in question run 
approximately north and south with their crests from 1 to 2.5 miles inland from 
the coast. Between Salifan and the higher mass of Tenjo to the north the terrain 
is depressed, and like the slopes of Tenjo itself it is open savanna or meseta, bearing 
no high vegetation suitable for Partule. Thus P. salifana is cut off from the north 
by this wide barren zone, wherefore its absence from the collections taken in the 
northern half of Guam is entirely natural. The vegetation of its area is continued 
southward along the high ground leading ultimately to Mount Sasalaguan, but no 
specimens were secured from the southern localities actually explored. To the 
eastward again the vegetation is more or less continuous along the river courses 
cut into the long slopes on that side of the mountain range; whether or not salifana 
exists in such places could not be determined. Its presence on the heights south of 
Mount Salifan is more probable than in the areas of lower altitude along the 
eastern rivers. 
The nurse plants are in no way unusual. Above the cogon grasses of the 
ascending slopes the bush begins abruptly at an altitude of about 700 feet and 
continues with few minor breaks to the summit (plate 4, a and B). Among the 
favored plants are the species of Pandanus which thrive here. Despite the seeming 
suitability of the conditions, only 118 adult snails of all species were taken by the 
author and his Chamorro companion, and this number 1s so small as to indicate a 
sparse Partula population in this region. Heavy rains had fallen during the two 
preceding days and nights, and on the day of the visit itself the skies were overcast 
and light rain was falling, thus permitting the snails to remain in more open situa- 
tions—facts which still further emphasize the relative scarcity of the animals in 
this place. 
A noteworthy general point is the similarity of P. salifana to the prevalent 
forms of the Society Islands and of other groups in Polynesia proper, which species 
are assigned by Pilsbry to the section Partula sensu strictu. The form of the shell 
and its heavier texture, exhibited even in half-grown examples, mark the resem- 
blance in question and contrast salifana with the other Guam species which con- 
stitute the section MARIANELLA of Pilsbry. From another standpoint the thickness 
of the shell is very important, because it is a feature exhibited by a species which 
lives where no limestone rock is found; in the next chapter it will be pointed out 
that P. fragilis possesses a very thin shell and it thrives in the northern region of 
calcareous rock. Obviously in neither case does the soil’s nature exert a direct 
effect upon the density of the shell. 
