132 U.S. NATIONAL MUSEUM BULLETIN 244 



broader than long. Meso- and metathoracic tibiae with minute 

 apical spur. 



Wings very sparsely scaled, semitransparent, membrane more 

 opaque than in other species. Forewing R2 stalked with R3+4; 

 discal scales, when present, very narrowly oblanceolate with acute 

 tips. Hind wing usually with M2 and 3 stalked for considerable 

 distance, separating just before margin. Wing expanse 20-33 mm. 



Male genitalia. — (Fig. 295.) As described for genus. 



Female. — Length approximately 22 mm. As described for genus. 



Female genitalia. — (Fig. 318.) 



Case.— (Figs. 113, 114.) Length 30-40 mm.; diameter 6-8 mm. 

 Somewhat variable in appearance, completely covered by small, flat, 

 firmly attached fragments of leaves, or by short (usually less than 6 

 mm. long) sections of twigs laid obliquely on bag and somewhat spirally 

 arranged. All possible intergrades exist between two conditions. 



Type. — In the American Museum of Natural History. 



Type locality. — Mojave Desert, California. 



Recorded hosts. — "Fabaceae: Prosopis sp.; Zygophyllaceae: 

 Larrea tridentata (D.C.) Coville" (Jones, 1928). 



Distribution. — (Map 5.) Known from the Intermontane Plateau 

 and Pacific Mountain Systems of the southwestern United States. 



Discussion. — Thyridopteryx meadi seems to be associated largely 

 with a single food plant, the extremely abundant "creosote bush," 

 Larrea tridentata, of our southwestern deserts. This shrub is capable 

 of surviving long periods of drought; it grows over extensive areas, 

 often in almost pure strands, from southern California to southwestern 

 Texas and thence south into Mexico. 



With the information available from various correspondents of the 

 late Dr. Frank M. Jones, especially Dr. C. T. Vorhies, formerly of the 

 University of Arizona, it is apparent that the life history of T. meadi 

 is quite variable. This fact is important not only in understanding the 

 seasonal fluctuation of the insect but also in contributing to a better 

 understanding of the life histories of other psychids, in particular 

 Thyridopteryx ephemeraejormis . 



As Larrea tridentata responds to rainfall with new vegetative growth, 

 the life cycle of T. meadi likewise is speeded to maturity by the presence 

 of moisture and more abundant, succulent food. During periods of 

 drought the larvae become lethargic. Vorhies observed some larvae 

 that suspended and closed their cases in mid-September as if for pupa- 

 tion; in July of the next year they were still larvae and had not moved 

 or opened their cases although apparently still in healthy condition. 

 He further noted that sprinlding egg-filled cases with water re- 

 sulted, within a few hours, in the hatching of the enclosed eggs. In 

 one limited area of dense infestation, where newly hatched larvae 



