DISTRIBUTION AND MIGRATION OF I.INEATA GROUP. I" 



barrancas. It does not seem to extend outside of these limits, but is dis- 

 tinctively a cliff and talus-slope form. Just whatrelatiou this species has to 

 the preceding from the standpoint of distribution it is impossible at present 

 to saw 



LEPTINOTARSA SIGNATICOLLIS. 



Apparently this species and the two preceding ones nowhere occupy the 

 same locality. The data of its distribution would indicate this, and, although 

 they are closely related, I have nowhere been able to find them living together. 

 Like the two preceding species, this one is an inhabitant of a particular 

 portion of the country. On plate I is shown the general distribution, where 

 it is represented as limited to the western side of the Rio Balsas Valley, and 

 on plates 3 and 4 are shown photographs of the habitat and its relation to 

 the general physiographic features of the country. It occupies the northern 

 and eastern tributary valleys of the Rio Balsas system, between the altitudes 

 of 4,000 and 5,500 feet. This distribution embraces the lower portion of 

 the Mexican escarpment, many of the great washes, as at Cuernavaca, and 

 the upper portion of the lower country leading up thereto. 



L. signalicollis, like undecimlincata, is confined to a narrow local habitat. 

 Its food is Solatium sp. , and it lives in colonies which continue in the same 

 place from year to year. The general habitat best adapted to this species is 

 similar to that occupied by undecbnlineata, and is shown in plate 4. The 

 favored locality for a colony is usually a growth of its food plant upon or 

 near the edge of a small stream or ditch, cut somewhat deep into the soil 

 of the flatter portiou of the valley floor, or on the upper slopes of the larger 

 barrancas (plate 3). It is rarely found near the edge of the smaller barrancas, 

 or at the foot of the hills. 



The rigid restriction of both the food and the beetles to a narrow habitat 

 tends to produce a band or zone upon either side of the valle3'S in which, at 

 points where the proper conditions have beeu developed by the side streams, 

 colonies of signaticollis are found. This band or zone is in some cases rather 

 sharply drawn, as at Cuernavaca, and less rigidly in others, as in the region 

 of Atlixco and Matamoros. The difference is, however, one of topography. 

 At Cuernavaca the topography is sharp and decisive ; at Atlixco and Mata- 

 moros it is more open, less rugged, and the zone of possible habitat formation 

 is much broader and correspondingly less distinct. This restriction to so 

 narrow a habitat has resulted in isolation, often of great intensity ; but this 

 has not brought about local variation, so that each valley shows the same 

 peculiarities seen in adjacent ones. The intense isolation and segregation 

 has not been of any apparent utility in the production of local forms or 

 races of L. signaticollis. 



As far as I am able to observe, the same method of dispersal is found in 

 signaticollis as in the preceding species, but I have not had an opportunity 

 to study its method of spreading over a new area. 

 2 T 



