58 The Mechanism of Evolution in Leptinotaesa 



rated by two deep barrancas from the rest of the valley; stock No. 619, from 

 sides of deep barranca between Cuernavaca and San Anton; stock No. 621, 

 from the top of the loma between the barrancas north of trail from El Hacienda 

 to Tetlama. (b) Atlixco: Stock No. 615, from cultivated fields 2 kilometers 

 to south of town, (c) Oaxaca : Stock No. 607, from foot of Maote Albans, on 

 rolling, well-drained area ; stock No. 605, from north and west sides of Cerro 

 del Fortin, to northwest of Oaxaca City. 



BlOTYPES. 



Four biotypes are capable of being developed from some strains of this species, 

 especially those from the northern and eastern edge of its range : L. oblongata 

 V, red elytral ground-color; L. oblongata b', orange elytral ground-color; L. 

 oblongata V, yellow elytral ground-color; L. oblongata b*, white or pale yellow- 

 white elytral ground-color. These are especially prone to develop in material 

 from that portion of the habitat along the south flank of the Nevada de Toluca, 

 but I have not been able to develop them from materials obtained in the Oaxaca- 

 Guerrero Highlands. 



LePTINOTABSA EUBICUNDA NOV. SP. 



(Plate 4, fig. 7.) 



Leptinotarsa ruMcunda, Tower, 1906. Inv. Evol. Chrys. Beetles, genus 

 Lept.; Carnegie Inst. Wash. Pub. No. 48, pp. 7, 21. 



The history of this form as I have found it leaves me greatly in doubt as to 

 what status it should have in this taxonomic orientation. When first found in 

 1903 it occupied a considerable range on the plain between Toluca and the 

 Nevada de Toluca, and the Sierra de Las Cruces, covering an area estimated at 

 10 to 12 miles square. It differed constantly in all stages from L. multitceniata- 

 variabilis, and was not observed inter-breeding with it at any time. In cultures 

 it is genetically constant and true to type indefinitely, and it genetically perpetu- 

 ates itself in nature in the same constant manner. In 1906 I was able to find it 

 only in a limited area of about half an acre in extent near Mexicalicingo, and 

 in 1908 only 30 specimens could be found in a week's search at the height of the 

 season, and in 1909 and 1910 no trace of the form could be found. The last 

 members of the race were as constant and were in all respects like the first 

 found, and while never abundant at any time, it was fairly easy to discover 20 to 

 50 in a day's search, and it was obtained in the earlier years in considerable num- 

 bers. Its rapid decline and apparent extinction raise some interesting questions. 



Because of its genetic distinctness and constant differences from the obviously 

 near relatives I have retained it here as a species. Future information may 

 change this orientation. 



Description of Living Animals. 



Imago: Broad, rounded, convex, dark red or crimson, with heavy, shiny 

 black color pattern. Above : Epicranium, pronotum, and elytra uniform deep 

 red or crimson, never orange or yellow; epicranium evenly punctate with dis- 

 tinct pits, anterior lateral epicranial spots fused and reaching anterior border, 

 rarely prolonged caudad; lateral posterior epicranial spots forming band on 

 posterior portion and anteriorly to eyes ; eyes black ; mouthparts black, polished, 



