456 INSECTA. 



PACHYSTOMUS, Lntreille, 



AVTiCTC the antennie are composed of three joints, the last of which is divided 

 into as many rings. 



In the second section, that of the Decatoma, Lat., we find the antenna? always 

 composed of three joints, the last of which, the longest, without stilet or seta, 

 and divided into eight rings, is clavate in some, and almost cylindrical or in 

 the form of an elongated cone in the others. The wings are usually incumbent 

 on the body. The tarsi are furnished with three pellets. 



These insects may be united in one generic section. 



XYLOPHAGUS. 



In Xylophagus proper, the body is narrow and elongated, and the antenmc 

 are evidently somewhat longer than the head, and terminated by an almost 

 cylindrical joint. The head is short, transversal, and without any particular 

 elevation anteriorly. 



In the third section Strut iomydes, Lat, we also find antennie consisting 

 of three joints, the last of which, exclusive of the stilet or seta, presents at 

 most five or six rings. This stilet, or that seta, exists in almost all of them, 

 and in those where they are wanting, the third joint is elongated and fusiform, 

 and always divided into five or six rings. The wings are always incumbent 

 one on the other. In several of those species where the antenna' terminate in 

 a somewhat oval and globular club, and always furnished with a stilet or a 

 seta, the scutellum is not spinous. 



This section comprises the genus 



STRATIOMYS, Geoffroy. 



In Stratiomys, properly so called, the antennse are much longer than the 

 head, the first and last joint being greatly elongated; the latter is fusiform, or 

 resembles a narrow and elongated club, narrowed at both ends, consisting of at 

 least five distinct rings, without an abrupt stilet at the extremity. The two 

 rings that compose it are not distinguished from the others by any sudden 

 contraction. 



The body of the larvse is long, flattened, invested by a coriaceous or firm 

 skin, and divided into annuli, of which the three last form a tail terminated by 

 numerous plumose hairs which radiate from the extremity. They inhabit 

 water. 



Our second general division of the Diptera, which are provided with a 

 sucker enclosed in a sheath, and whose antenna? consist of but two or three 

 joints, comprises those whose proboscis, usually bilabiate, long, geniculate, and 

 bearing the palpi a little above the elbow, is most commonly entirely contained 

 in the oral cavity, and, when always salient, has a sucker composed of only two 

 pieces. The last joint of the antenna?, always accompanied by a stilet or seta, 

 never exhibits annular divisions. The palpi, when it rest, are concealed. 



