l.AF?VAL FORMS OF f'OLEOPT?:RA 



lary articulating' area large and cushioned ; hypopharyngeal 

 seloronios nsvniiiiptrical, strong, and much differentiated 



Ddscillidae (DasciUus) (pi. 63 

 A-I) 

 Tenth abdominal segment well-developed, with soft, terminal, 

 un])aired, two- jointed, and retractile prolongation (anus 

 jjlaced immediately below ninth abdominal tergite) ; five 

 ocelli on each side; antenna short; maxillary articulating 

 area rather small and indistinct; hypopharyngeal scleromes 

 symmetrical, of moderate strength, and not very much dif- 

 ferentiated Heteroceridae^'^ (pi. 64 A-M) 



3. Spiracles vestigial or absent, except an annuliform pair on 

 eighth abodminal segment ; three terminal tufts of gills re- 

 tractile into a pocket without an operculum ; antenna mul- 

 tiarticnlate and very long; one large ocellus and one small 

 ocellus on each side (Mandible dimorjDli) 



Helodidae (pi. 65 A-H) 

 Spiracles all present and bif orous ; gills absent ; antenna three- 

 jointed and of moderate length ; five ocelli on each side 



Xosodendn'dae^^ (pi. 66 A-P) 



J. DRYOPOIDEA 



This series does not conform with the series named Dryopoidea 

 in the classification of the imagines but it has been considered ex- 

 pedient to retain the old serial name in the present tabulation of 

 several families which according to the larvae are associated with 

 the genus Dryops. 



Key to Families and Subfamilies 



1. Terminal cloacal chamber and movable operculum absent 2 

 Terminal cloacal chamber present and furnished with three 



tufts of retractile gills and with a movable operculum below 

 ninth abdominal tergum 5 



2. Body cylindrical; Avithout ventral gills (except in an Asiatic 



larva probably belonging to the Ptilodactylidae) ; spiracles 



bif orous 3 



Body flat, broadly oval, limpetlike; with five pairs of ventral 

 gills freely exposed from second to sixth abdominal seg- 

 ments ; spiracles annuliform 4 



3. Antenna comparatively long; tenth abdominal segment with a 



pair of large lobes usually carrying spinose cliverticles. (In 

 ^'* The family Ileteroceridae is usually placed, according to the 

 characters of the imagines, in the series Dryopoidea. 



■'■' The taxonomic i)ositi()n of this family is much debated but, 

 according to the characters of the imagines, it is usually placed in 

 the series Byrrhoidea. 



44 



