144 LEPIDOPTERA OF NORTH AMERICA. 



ure takes a transverse course, throwing off near its centre, 

 the disco central, and joins the submedian at the origin of 

 the medio-superior nervule; in addition to this, the median 

 throws off more posteriorly the medio-central and posterior 

 nervules. Lastly, near the inner margin is found the sub- 

 median nervure, which is simple and usually bifid at the base. 



In the posterior wings, the costal riervure is simple and 

 prolonged to the hind margin, and is connected with the 

 subcostal towards the base, by a short intercostal nervule. 

 The subcostal nervure subdivides into two branches, the 

 apical and postapical ; the discal nervure arises at the bifur- 

 cation of the subcostal, and emits the disco-central nervule 

 about its centre, and anastomoses with the submedian at the 

 origin of the medio-superior.' The median nervure is nearly 

 straight, but angulated at the origin of the medio-central, 

 and posterior to this point throws off the medio-posterior. 

 The submedian and internal nervures are both simple. 



This pterogostic structure, without undergoing any essen- 

 tial variation whatever from the type, is found in all the 

 genera of the group. 



The abdomen is usually cylindrico-conical, longer than the 

 posterior pair of wings, sometimes tufted at the tip, and each 

 of its segments are furnished on the posterior edges with a 

 row of acute spinules concealed by a covering of scales. 



The legs are usually long and strong, and the under sur- 

 face of the tarsi roughened with numerous, acute, rigid spin- 

 ules and furnished with a pair of free, simple claws. The 

 anterior tarsi have a long single spur on the inner surface, 

 the middle a terminal pair, and the posterior two pair. 



The eggs of the perfect insect are deposited singly on the 

 food-plants of the larva?, which are usually conspicuous in 

 size when full grown, and live a solitary life. They have 

 naked, cylindrical bodies, varying slightly in form, and pre- 

 senting, usually, differences of ornamentation in the several 

 genera. They possess eight pairs of feet, three of which are 

 thoracic, four abdominal, and one terminal ; the latter are 

 large, strong, and almost square, with the plantoe situated at 

 the anterior angle. On the dorsum of the eleventh segment 

 is placed a rigid spine, called the caudal horn, and when this 

 is absent it is replaced by a lenticular tubercle. 



The pupce are cylindrico-conical, with the extremity of the 

 abdominal case terminating in single, stout, acute spine, and 

 is contained in an imperfect cocoon, or near the surface in a 

 cell, or in a subterranean cell. 



