534 The American Naturalist. [June, 
established Bahaman species has become further divided into 
several insular races. 
The genus Geothlypis is not found in the West Indies, and we 
are forced to consider the very distinct Geothlypis trichas ignota 
of Florida as the probable ancestor of the rostrata group. The 
supposition becomes more probable when we consider that 
ignota, in having a larger bill and more yellow below than the 
North American Geothlypis trichas, thus presents a distinct step 
towards the Bahaman species. In other words, although more 
nearly related to ż¿ríchas, ignota is in a degree intermediate 
between it and rostrata. We dwell on this because the origin of 
the Bahaman bird is of special importance, although being 
evidently derived from the Florida form, it more nearly resembles, 
indeed is very similar to, Geothlypis beldingit of Lower California. 
Thus we find that quite independently of each other two birds 
whose habitats are separated by a continent have been evolved to 
almost specific identity. This instance is of great value in study- 
ing the relations of island faunæ, where the same type may 
appear on widely separated islands, and be replaced on intervening 
islands by a nearly related but still different species. We have 
noted somewhat similar cases in our remarks on Spindalis and 
Vireo crassirostris and Certhiola. May we not assume here that ~ 
the intervening species is a common ancestor, and that by similar 
lines of divergence two forms have been produced which are more 
nearly related to each other than they are to the parent stock ? 
23. Polioptila cerulea cesiogaster—A form differing very i 
slightly from P. cærulea, which occurs both in Florida and Cuba. fo 
24. Mimocichla plumbea—A species closely related to Mimo- 
cichla schistacea of Cuba. 
List oF Brrps PECULIAR TO THE BAHAMAS, WITH THE SPECIES 
WHICH THEY APPARENTLY REPRESENT. 
BAHAMAN SPECIES. REPRESENTED SPECIES. 
Rallus coryi, Rallus longirostris group (Continental). 
Ardea bahamensis, Ardea virescens (Continental). 
Coccyzus minor maynardi. Coccyzus minor (Tropical). 
Saurothera bahamensis. Saurothera vieillotii (Porto Rica). 
