GENERAL FEATURES OF POLYNESIAN REALM IN RELATION TO DISTRIBUTION. 15 
subsidiary area, inasmuch as two-fifths of all of the definitely located species 
reside in that group alone. ‘To the northwest the numbers of species in the several 
groups decrease rapidly, although the suitable islands are in no wise diminished in 
number or area. The solitary species from Malaysia is remarkable, in view of the 
distance that separates its island from the nearest types, those of the Caroline 
Islands. Possibly further exploration will bring to light new forms that will fill in 
the existing wide gap. 
GEOGRAPHICAL AND GEOLOGICAL FEATURES OF THE SOCIETY ISLANDS. 
The group named the Society Islands by Captain Cook comprises fifteen ele- 
ments of different extent and constitution. The location, geological nature, and 
other features of these islands are given in text-figure 1 and in table 2. Like that 
of the whole area, the outline of this group is an ellipse whose longer diameter 
trends from south-southeast to north-northwest. Within this outline the islands are 
grouped in the Windward and Leeward divisions, of which the former lies toward 
the southeast, the point from which the prevailing winds blow. 
TaBLE 2.—General description of the Society Islands. 
| Approximate} Approximate |Approxi-| No. of 
Subgroup. Island. Character. latitude, longitude, mate species of 
center. center. extent. | Partula. 
o Y 2 UY sq. Mm. 
Mahititnrtamver ier WOE, s5000000000 lif SOS: 149 25 W. 350 8 
Moorea. ese Wiol Can Caaeeeennn ily SOS, 149 49 W. 40 4 
Windeard Mehetia. es ircoeeie Volcanic. Oe IA Lite BAD Os 148 7 W. 5 Sy 
**|) Maiou-iti....... Volcanic andcoral...| 17 38S. 150 37 W. 3 
MetiarOa' yas sreras| WACO scree icra ove ld 38 149 35 W. 2 
Makatea........| Uplifted limestone...| 15 48S. 148 16 W. 5 
Euahine series WOMB oconccco000| 16 45S 150 59 W. 19 5 
Raiatearniere ase WOE 50000000006 16 50S 151 25 W. 60 21 
PRahaarse yet ckesss WOMEINC cscoc0000000 10 87S 151 28 W. 32 5 
Borabora....... Volcanic and coral...| 16 30S 151 44 W. 8 1 
Leeward....|; Maupiti........ Volcanic and coral...) 16 27S 152 12 W. 11 se 
INOW, Co 00008 ACO yee ee 16 IOS 151 49 W. 6 
Mopelia........ ACO Scie pens eteterier steve 16 59S 153 58 W. 4 
Scillyaneneneneiec ATOM AAs eerie 1OmeZiaS 154 44 W. 4 
Bellingshausen. .| Atoll............... 15 46S 154 32 W. 3 
Tahiti (plate 9) is the largest member of the group, having an approximate area 
of 350 square miles. While its detailed structure will be described at a later point, 
its general features demand consideration here for the sake of their comparison 
with the characteristics of the other islands. It is a double volcanic mass whose 
greater and lesser parts—Tahiti nui and Tahiti iti or Taiarapu—are connected by 
the low and narrow isthmus of Taravao. The larger part has almost the form of a 
pentagon whose longest diameter is about 25 miles; its circumference is about 75 
miles. Taiarapu is nearly 15 miles in length, with a circumference of 45 miles. 
Each part is an independent volcanic massif with a great primary crater basin, and 
with subsidiary vents outside of this. The greatest height of Tahiti nui is 7,500 
feet, and that of Taiarapu is a little less than 4,000 feet. 
To the same class of “high” islands belong Moorea, Huahine, Raiatea and 
Tahaa, and Borabora, which, with Tahiti, constitute the series of six islands 
inhabited by species of the genus Partula. Moorea (plate 2), formerly cailed Eimeo, 
