336 TRANS. ST. LOUIS ACAD. SCIENCE. 



p. 369). None of the Helerocerous borers, so far as my experi- 

 ence goes, line their burrows continuously with a matting of silk ; 

 but use the silk very sparingly, or not at all, till about ready to pu- 

 pate. The larva of Yuccce, for the most part, lives in a tube of silk, 

 which it builds and extends often several inches beyond the trunk 

 or stem in which it burrows, and from which it often, especially 

 when young, issues to feed. In this, again, it approaches the 

 Hesperians, which are partial concealers, and live, when not 

 feeding, within silken cases or tubes constructed among the leaves 

 of their food-plants. 



The pupae of the Castnians, like those of all Heterocerous 

 borers known to me, are, according to authors, armed with rings 

 of minute spines on the hind borders of the abdominal joints — 

 the spines serving a very useful purpose in assisting the pupa out 

 of its cocoon. Heterocerous borers also pupate in a more or less 

 perfect cocoon, made either within or without the burrow ; and, 

 in the issuing of the imago, the mesothoracic covering generally 

 collapses, the leg-cases become unsoldered, and those of the an- 

 tennae are always separated and often curled back over the head 

 in the exuvium. The Hesperians pupate* within the silken cavity 

 occupied as larva, or else in a separate slight cocoon : the pupa 

 is generally attached to a silken tuft by the hooks of the cremas- 

 ter, and sometimes by a silken girth around the middle of the 

 body besides : it is not ^infrequently covered with a slight pow- 

 dery bloom, and is characterized by the prominence of the pro- 

 thoracic spiracle* : the exuvium more nearly retains its form, 

 the leg-cases remaining soldered, and even those of the antennae 

 being rarely separated. In not having a well-formed cocoon, in 

 being covered with bloom, in the characters of the exuvium, in 

 the conspicuity of the prothoracic spiracle, but more particularly 

 in the want of minute spines on the borders of the abdominal 

 joints, Yuccce is again Hesperian and not Castnian. Indeed, 

 except in the broader anal flap, densely surrounded with stiff 

 bristles, in place of an apical bunch of hooks, in the smaller head 

 and larger body, it resembles Nisoniades in general form, color, 

 and texture. 



The typical Castnians, in the perfect state, have the wings large 



* In Nisoniades Juvenalis (Fabr.) this spiracle takes the form of a prominent sooty- 

 black horn or tubercle. 



