﻿NORTH AMERICAN SPHINGID^. 125 



stalk is distinctly prismatic, and the articles are ciliated or bear short pectinations in 

 the males. The eyes are usually large, hemispherical and salient, and the palpi have 

 the third article reduced to a mere point, placed on the summit of the well developed 

 second article. The tongue is usually well developed, and nearly equal to the 

 length of the body ; in some instances it is more than twice longer than the body, 

 and in others it is almost obsolete. 



The thorax is always well developed and large, containing powerful muscles, that 

 are attached to elongated, narrow and dense wings, the inner border of which is much 

 shorter than the exterior, in consequence of the obliquity of the hind margin, and 

 are attached to each other by a bristle and hook. They are characterized by the 

 following peculiarities of structure. {See figures 1, 2.) The basal portions of the 

 marginal and costal nervures are thick and strong, and contiguous to each other and 

 the subcostal nervure ; these and the subcosto-marginal nervules proceed towards the 

 apex of the wing almost like a bundle of rods, thus forming an external margin 

 capable of resisting rapid and strong vibrations upon the atmosphere. In addition 

 to the two marginal nervules, given off from near - the posterior-superior angle of the 

 disc, the subcostal divides into a subcosto-apical, post-apical and inferior nervules. At 

 the origin of the subcosto-inferior, the discal-nervure takes a transverse cousre, throw- 

 ing off near its center, the disco-central, and joins the submedian at the origin of the 

 medio- siiperior 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 

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



In the posterior wings, the costal nervure 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 post- 

 apical ; the discal nervure arises at the bifurcation 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 essential 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 surface of the tarsi roughened 

 with numerous, acute, rigid spinules 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. 



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