24 INTRODUCTION 
coast extend from Cape Cod northward; the American, from 
Cape Cod to Cape Hatteras; the West Indian, from Cape Hatte- 
ras southward. On the Pacific coast the divisions, without defi- 
nite names, are from the Isthmus to Acapulco, Acapulco to the 
Gulf of California, Cape Lucas to the Strait of Fuca. These 
divisions merge at indefinite lines, but the above limits are 
generally accepted as the points of broad division. 
The shore or littoral fauna is especially abundant and com- 
prises more species that are curious in form and beautiful in 
color than the others. The invertebrates of the deep sea are 
mostly transparent and of a blue or violet tint, while the fishes 
are gray or bluish above and white beneath, which renders them 
inconspicuous to their enemies. 
