1 8 DISTRIBUTION AND DISPERSION OlP LEPTINOTARSA. 



LEPTINOTARSA ANGUSTOVITTATA. 



The relation of this species to environmental complexes can not at present 

 be discussed. It is known from only a few localities, is never abundant, and 

 I have never been able to study it to any extent in nature. The fact, however, 

 that I have reared it in experiment from imdecimlineata and that it is inter- 

 mediate between undccimliiieata and signaticollis , is suggestive, but its full 

 significance must await experimental elucidation. 



LEPTINOTARSA MULTITAENIATA. 



This species, like imdecimlineata, is a central one about which closely 

 related species are grouped. The data of its distribution is given on page 

 7, and on plate i is plotted its distribution. It is limited to the Valley of 

 Mexico, the Plains of Apam, and the flat mesa southward to Puebla and 

 Matamoros in Puebla ; eastward it extends to the foot of the Sierra Madre 

 Orientale, and northward to about 20° 30" north latitude. It is everj^where 

 confined to the level country, never being found in the lowlands nor upon 

 the mountain sides. 



The area which is the habitat of this species is distinct topographically, 

 being sharply marked off from the rest of the Mexican Plateau. It is level, 

 but is surrounded by high hills and mountain chains with volcanic peaks to 

 the east, south, and west, and cut off by a rugged range to the north. It is 

 highest in the Valley of Mexico (7,400 feet), sloping southward to Puebla 

 (7.091 feet), and rising slightly towards the Sierra Madre Orientale. It is 

 practically level, with a variation of only a few hundred feet in altitude. 

 Over it are scattered low hills, often of volcanic origin, small volcanic cones, 

 eroded necks, and lava flows with steep sides covered with talus. The 

 streams, which are all of small size, have beds deeply cut from 10 to 50 or 

 100 feet in depth, with perpendicular walls in a stiff, sticky deposit of modified 

 volcanic ejecta. The drainage is largely to the south, through the Rio 

 Atoyac into the Rio Balsas syvStem, and to a limited extent to the northeast 

 and east through the short Gulf coast streams. 



The rainfall is least in the lee of the Sierra Madre Orientale, where pine 

 barrens and semi-arid grassland conditions are extensively developed ; it 

 increases gradually to the westward, and is largest in the Valley of Mexico. 

 The northeast trade winds, striking the high eastern mountains, lose the 

 greater part of their moisture upon the eastern slopes and pass over the 

 mountains as cold dry winds, bringing but little moisture to the eastern 

 portion of the country, which is always semi-arid. To the westward these 

 winds become warmer and more moist, and the rains more abundant, until 

 in the Valley of Mexico the rainy season has copious dail}^ showers. 



This region is a rather old land area which had stood fol- a long time at a 

 much low^er altitude and had been worn down to base level with residuals 

 about it. Subsequent volcanic action and mountain building produced 



