GEOGRAPHICAL DISTRIBUTION OF THE GENERA. 241 



Echinanthus ranges over an area included within the range of Cidaris, Echi- 

 nometra, etc. And in this same Plate (C) the range of Astriclypeus and 

 Faorina, of Arachnoides, Peronella, etc., of Holopneustes, Amblypneustes, 

 etc., is considered sufficiently approximate to be indicated by the same color. 

 In PI. E the range of Hipponoe' and Toxopneustes is included within the 

 limits of the range of Brissus, Lovenia in its turn being included within 

 the limits of the range of Hipponoe and Toxopneustes. These examples 

 will suffice to explain the method adopted to show the geographical distri- 

 bution of genera. Where the localities are in the least doubtful, they have 

 been omitted in the representation of the distribution of the genus on the 

 maps, as in the case of the occurrence of Moira on the Pacific coast of Mex- 

 ico, and of Mellita and Moira in the Red Sea. Other genera, consisting of 

 but single species of a limited or doubtful range, have also been omitted. 

 They are few, however, and the maps include every genus which is well 

 characterized, the distribution of which can be tolerably accurately ascer- 

 tained from the range of its species. 



