PHILIP P. CALVERT 375 



specimens measured. Each pit is smooth within, shining black 

 and its external or lateral end usually produces an emargination 

 on the inner or mesal edge of the pale spot present on each side 

 of the dorsum of this lobe. 



The usual statement is that in the pairing of the Zygoptera the 

 inferior appendages of the male are applied cephalad of the hind 

 prothoracic lobe of the female, his superior appendages caudad 

 of that lobe. If this be true for the species here discussed, these 

 dorsal pits of the female may receive the inferior appendages of 

 the male. Since the former are much larger than the apices of 

 the latter (c/. figs. 5 and 7 with 16, 17 and 20, 21, plate XXXIII), 

 the adaptation does not appear to be verj^ exact. 



Enallagma cultellatum, although suggesting the pollutum-trun- 

 catum group by the superior appendages of the male, has the 

 black on the dorsum of abdominal segment two not reaching to 

 the base, the pale postocular spots not connected, the mesostigmal 

 lamina not so ridge-like and without any mesal tubercle, abdom- 

 inal segments eight and nine both pale blue dorsally in the male. 



The female of E. cultellatum has a pair of pits on the middle 

 prothoracic lobe, but they are much smaller and shallower than 

 in the other species here discussed and are situated nearer to the 

 hind lobe, which latter is quite different from the hind lobe of our 

 species in question being trilobulate instead of entire, the middle 

 lobule a little posterior to the lateral two and with a horizontal 

 ridge projecting from its hind surface. 



The following pages give the chief differentials of these six 

 species. The dimensions of the width of the various stripes on 

 the thorax refer in each case to the width at mid-height. Only 

 in the cases of pollutum, laurenti and vesperum does it seem 

 desirable to quote the existing literature. 



The males may be distinguished by the form of the terminal abdominal ap- 

 pendages, shown on Plate XXXIII, figs. 12-2;}, and by the following color 

 differences : 

 Dorsum of abdominal segment nine pale blue or orange. 



Pale postocular spots directh" confluent with the pale color of the rear of the 

 head, middle prothoracic lobe predominantly pale on dorsum., .laurenti 

 Pale postocular spots not directly confluent with the pale color of tlie rear 

 of the head, although they may be indirectly confluent therewith ria the 

 pale transverse stripe which connects the postocular spots with each other; 

 middle prothoracic lobe predominantly black on dorsum. 



TR.\NS. AM. ENT. SOC, XLV. 



