238 [October, 



very far off, in areas approximately of similar extent to the 1907 locality 

 it was common, but not, perhaps, so abundant as I had seen it in 

 1907. I think I may say that the 1914 area was practically un- 

 inhabited by full-grown cases of the species in 1907. I did not, of 

 course, in 1907, go over the 1914 locality, saying I will take a note 

 of this against what I may find in 1914, but I did go over much of it 

 in order to gain some idea of the limitations of the distribution of 

 the species in 1907. 



I may add that in both years I met with a very few cases less 

 than half grown that no doubt dated from the preceding year, and 

 would mature in the following one. These small cases were very in- 

 conspicuous, and most examples were probably close to the ground 

 under the herbage, so that they were probably abundant though I saw 

 so few. 



These facts strongly support the observations of M. Eondou, that 

 this and other species of Psychids in the GTavarnie district have a life 

 cycle of two years, and that in alternate years they appear to be absent 

 from localities where they are not uncommon. As regards pyrenaella, 

 there are localities where it occurs in the even years (1914) and others 

 where it occurs in the odd years (as in 1907). 



In the Val d'Ossoue it would appear that thei-e is an even year 

 area in close proximity to an odd year one. Of course, my observations, 

 with a seven years' interval between them, might be explained in various 

 other ways, but the one suggested agrees with M. Eondou's prolonged 

 studies of these Psychids in this and other portions of this very 

 interesting district. 



I may digress so far as to express a wish that M. Eondou would 

 publish some of the many interesting facts as to the insects of the 

 central Pyrenees with which he is familiar. For example, several years 

 ago I worked out a good deal of the life-history of L. orbitulus, and 

 was unaware that its food-plant was known. M. Eondou had, however, 

 found the larva on Androsace (Gregoria) vitaliana, and had bred it some 

 years before. 



These instances of species being common in alternate years and 

 absent in the intermediate ones, which are recorded of various 

 Lejndoptera besides these Psychids (the 17 year Cicada is an extreme 

 example of the same phenomenon), seem difficult to understand, since we 

 know that many species easily add a year to the time necessary to their 

 transformation, and one would suppose that the species would be 



