74 AN INTRODUCTION TO ENTOMOLOGY. 



TABLE OF SUB-FAMILIES OF LIBELLULID^.* 



A. Wings alike, vertically folded in repose. (Eyes remote and peduncled.) 

 B. Antecubital cross-veins numerous, at least five in number. (Wings al- 

 most always not petiolated.) i. CALOPTERYGIN^E. 

 BB. Antecubital cross-veins two only. (Wings always distinctly petiolated.) 



2. AGRIONIN,E. 



AA. Hind wings differently shaped from front wings ; all four wings carried 

 horizontally in repose. 



B. Antecubitals of the first and second series not corresponding except at 



base. Base of second series of postcubitals with cross-veins. 



C. Eyes remote. 4- GOMPHIN^E. 



CC. Eyes touching at a single point, the touching part of each forming an 



acute angle. 5- CORDULEGASTERIN^E. 



CCC. Eyes touching for a considerable space, the touching part straight, 



or at a single point (^Eschina heros), the touching part rounded in a 



single curve. 3. ^ESCHIN^E. 



BB. Antecubitals of the first and second series corresponding. Base of the 



second series of postcubitals with no cross-veins. 



C. Each eye laterally tubercled behind. 6/CoRDULiN^:. 



CC. Posterior edge of each eye simple. 7. LIBELLULIN^E. 



CALOPTERYGIN^E. There are only two genera of this sub-family repre- 

 sented in our fauna. In Calopteryx the wings are very broad, and the basal 

 <;pace has no transverse veins. Hetarina differs in having the wings rather 

 narrow, and with the basal space reticulated. In this genus the base of the 

 wings in the male is blood-red. 



AGRIONIN^E. The greater number of our species belong to Lestes and 

 Agrion. In Lestes the median and subnodal sectors arise from the principal 

 sector nearer the arculus than the nodus ; while in Agrion these sectors arise 

 under the nodus. 



. The greater number of our species belong to the typical genus 

 In the males of this genus the anal angle of the posterior wings is 

 acute, the lower anal appendage is usually triangular, and the second abdom- 

 inal segment bears upon each side a little ear-like tubercle. Of the genus 

 Anax we. have one common species, A. junius. This is a large insect, measur- 

 ing in length 68-74 mm., and having an alar expanse of 104-110 mm. In the 

 males of this genus the anal angle of the posterior wings is rounded like that 

 of the females; the lower anal appendage is short and truncate; and the 

 second abdominal segment has not ear-like appendages. 



GOMPHIN^E. In the typical genus Gomphus the triangles of all of the wings 

 are without transverse veins ; this genus includes many species. In the genera 

 to which the following species pertain the triangles have transverse veins. 

 Tachopteryx thoreyivs a large insect expanding 100 mm.; it is remarkable for 

 the length of the pterostigma, which measures 9 mm. Hagenius brevisfylus is 

 an even larger species, which expands 104-1 14 mm. The pterostigma meas- 



* After B. D. Walsh, Proc. Ent. Soc. Phil. II. p. 259. 



