14 VARIATION, DISTRIBUTION, AND EVOLUTION OF THE GENUS PARTULA. 
existence of Partulez, are more or less isolated valleys, whose differing forms may be 
analyzed in correlation with their geographical and topographical proximity. In 
brief, then, the valleys and their diverse species constitute elements of a primary 
order, to be compared with one another; such elements taken together form an 
island-complex, which, as an element of a second order, may be contrasted with a 
similar complex of another island in the same association; uniting the several 
islands into a combination of a tertiary grade—the island group and its species— 
this may be investigated as a whole in relation to other combinations of the same 
status in different parts of the whole area. ‘The circumstances are such, then, as 
to give an unusual interest and significance to the investigation of the genus Partula 
and its distribution, on the basis of a systematic and detailed analysis not ordinarily 
possible when dealing with similar problems of zoogeography. 
GENERAL GEOGRAPHY OF THE REGION INHABITED BY PARTULA. 
The line circumscribing that part of Oceania which includes the islands inhab- 
ited by Partula has the general form of a long oval or ellipse (plate 1). The long axis 
of this ellipse begins in the neighborhood of the Society Islands, about Lat. 20° S. 
and Long. 140° W., and it extends in a north-northwesterly direction to the Marianne 
or Ladrone Islands, about Lat. 17° N., Long. 135° E.—a distance of approximately 
4,000 geographical miles. ‘There is a single record of a species outside of this 
ellipse, in the case of P. newcombiana Hartman, which is assigned to Salibabu of the 
Talauer Group, near Mindanao (Lat. 2° 2’ N., Long. 125° 40’ E.). The eastern- 
most inhabited group is the Marquesas, about Long. 138° W. The Ladrones mark 
the limit in northern latitudes, while the Austral Islands, about 23° S., are the most 
extreme islands below the Equator to be inhabited. 
TaBLe 1.—General distribution of the species Partula. 
Slelet (1) Amcicn tetarscec pinkie ob do cit coc’ 44 
| Marquesas yrs aac: kin nd he EE ee 6 
Polynesia...... Austral Cookxsshe ies ence ne 2 63 
SamMOan ee aereecvel yea eee erie 8 
Liiii, INO\ HEINE), WGC GG cooaKoDG00d0000 3 
New Hebrides, Santa Cruz............. 17 | 
5 Solomon nisin: ove eee ee Dee 11 
MASEWESE, oo 05 New Ireland, New Britain, Admiralty.... 37 
New Guinea, Louisiade................. A) 
PEL ews ee Sal Nate oa ee SO AE etaner ioe eee ee 3 
IMicronesianean\\Carolines perenne einnee nt Eeoee rein: 4 10 
Marianne irate soisia erehet sre eee toereie or eeietenee 3 
Malaysian shalauer(Salibabu) pees 1 1 
111 
According to Pilsbry, the authentic species which are definitely assigned to the 
several groups and divisions of Oceania number at least 111, distributed as indicated 
in table 1. The salient facts are that Polynesia proper is the present headquarters 
of the genus, and that the Society Islands form the most congested part of this 
