264. THE CHICAGO ACADEMY OF SCIENCES. 
humilis. On the north it barely enters the Boreal (Canadian) life 
zone. It occupies all of the Canadian, Upper Mississippian and Nova 
Scotian regions, and a large part of the Columbian, Coloradoan, Cali- 
fornian and Rio Grandian regions. It barely enters the Hudsonian 
region on the north. Its absence from the Great Plains area is note- 
worthy, but may be due to lack of records. 

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Distribution of 
MODICELLA 
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BrG. 25: 



*LOWER CALIFORNIA: Common in the ponds of Sierra Laguna, at some 
height. Before known as far south as latitude 31° 51° (Cooper). 
GEOLOGICAL RANGE? (Figure 26): Pleistocene. 
Comparing the geological distribution of modicella with the recent 
distribution, we find that it covers about the same territory. To the 
south the recent distribution extends farther into the Lower Austral 
life zone and to the north it penetrates the Boreal life zone. It is 
noteworthy that no fossils have been recorded from deposits in the 
latter zone, the species in Pleistocene time seeming to keep within the 
Transition life zone. This restriction of distribution may be, and 
1This record is doubtful as no specimens of true modicella have been 
seen from Mexico or Lower California. The specimens were probably Galba 
bulimoides cassi, which somewhat resembles modicella. As the record has not 
been substantiated, it is excluded from the map, though recorded here for com- 
pleteness. The original specimens were lost in the earthquake which de- 
stroyed the Mustum of the California Academy of Sciences. 
2It is probable that a number of records here listed were really based 
on Galba parva or some one of the related species, as all of the smaller Lym- 
nzeas have been lumped under humilis. It has been impossible to verify the 
majority of these records and they are, therefore, listed under modicella, 
