SIALIDAE 



447 



whole of the Palaearctic and Nearctic regions, and reappears in 

 Chili, 1 though absent in all the intervening area. Several other 

 genera of Insects exhibit the same peculiarity of distribution. 



The genera Corydalis and Chauliodes form a group distinct 

 from Sialis, and are totally differ- 

 ent in appearance, being gigantic 

 Insects, sometimes with the man- 

 dibles of the male enormously 

 elongated (Fig. 290). The species 

 of Corydalis are called in North 

 America Hellgrammites ; Eiley 

 has described and figured the 

 metamorphosis of C. cornutus? the 

 life -history being very similar to 

 that of our little Sialis. A mass 

 consisting of two or three thousand 

 eggs is formed by the female, and 

 the young larva has long fila- 

 ments at the sides of the body 

 like Sialis. These in the later 

 larval life are comparatively shorter, 

 but the Insect is then provided 



with another set of gills in the FIG. 290. Corydalis crassicornis, male, 

 form Of Spongy masses O11 the with Beater portions of the wings 



removed. Texas. (After il'Lachlan.) 



under -side of the body. Riley, 



however, considers that these organs serve the purpose of attach- 

 ment rather than of respiration. The 

 larvae are known to the Mississippi 

 fishermen as crawlers, and are greatly 

 esteemed as bait. 



The Eaphidiides or snake-flies form 

 the second tribe of Sialidae. There are 

 only two genera, JRapkidia and Inocellia, 

 peculiar to the Palaearctic and Nearctic 

 regions. The perfect Insects are chiefly 

 remarkable for the elongation of the 



prothorax and back of the head to form a long neck, and for 



the existence in the female of an elongate exserted ovipositor. 



1 JI'Lachlan, Ent. Month. Mag. vii. 1870, p. 145. 

 - Rep. Ins. Missouri, ix. 1877, p. 125. 



FIG. 29l.Raphidia notata, fe- 

 male. Britain. (After Curtis.) 



