SCHISTOCERCA, SPHINGONOTUS AND HALMENUS 413 



Hence the two species are separated from each other not by a differ- 

 ence in habitat, but by a difference of geographical location, /. e., one 

 species is confined to one group of islands and the other species to an- 

 other group. 



If we had no specimens from Duncan Island the two first described 

 forms of ScJiistocerca from the Galapagos could not be regarded oth- 

 erwise than as two valid and well-separated species. A large num- 

 ber of specimens from Duncan, however, present such an amount of 

 variation that they can be arranged in a closely graded series duplicat- 

 ing at one end the jnelanocera form and at the other the I iterosa form. 

 At first sight this would appear to reduce these two supposed species 

 to subspecies, but reasons will be given later for regarding the Dun- 

 can race as a hybrid. 



RACES OF SCHISTOCERCA. 



The specimens from the different islands show striking, though, in 

 most cases, slight differences distinguishing the individuals of each 

 island, as a race, from those inhabiting any other island. There are 

 two exceptions. Abingdon and Bindloe have the same form, and 

 Albemarle supports at least two races. Scudder was the first to 

 point out the existence of races on the islands, but his material was 

 alcoholic, and he could not, on that account, well describe such color 

 differences between them as exist. Moreover, he had no specimens 

 from Abingdon and Bindloe. 



The following are the diagnostic characters of the various races. 

 Detailed descriptions are given on pages 419-436. 



S. melanocera jnelanocera (PI. xxvii, fig. i). — Of large size; yel- 

 low of metazona contrasts strongly with black of prozona, yellow spot 

 on side of prozona distinct ; abdomen uniform ; terminal halves of 

 tegmina immaculate. 



From Charles Island. 



This race maybe regarded as typical of S. jnelanocera; and 

 Charles Island is most probably the locality of Stal's type of thespecies. 



S, jnelanocera jninor. — Smaller than the Charles form ; does not 

 differ from it in color. 



From Tagus Cove, Albemarle Island. 



S. melanocera pallida. — Same size as the Tagus Cove form, but 

 differs from this race in being of a generally paler color. 



From Barrington Island. 



vS, jnelajiocera Ihieata (PI. xxvii, fig. 5). — Differs conspicuously 

 from the Charles race in the presence of a distinct pale line along the 

 side of the abdomen on the lower edges of the terga. 



From Iguana Cove, Albermale Island. 



