No. 39] ODONATA OF CONNECTICUT: COENAGRIONIDAE 55 



A comparatively large genus represented in New England by 

 about 1 8 species. 



For literature on adults, see : 

 Calvert, P. P. Transactions of the American Entomological Society, XLV : 

 373-392: 1919, Plate XXXIII (limited to vesperum group). 



Biologia Centrali Americana, 1902, 103: 379, etc. 



See also publications of Calvert, Garman, Howe, Kellicott, and Needham. 



Synopses and treatises on the nymphs have been published by: 

 Garman, P. Bulletin of the Illinois State Laboratory of Natural History, 



XII: 517-559: 1917- 

 Howe, R. H. Memoir of the Thoreau Museum of Natural History, II: 



110-113: 1921. 

 Needham, J. G. New York State Museum Bulletin 68: 250-258: 1903. 



In general the Enallagiiias of New England may be grouped 

 together in several divisions as follows : 



1. The vesperuin-signatum group, containing signatum, pictum and ves- 



perum. Probably the most distinct of all the groups and charac- 

 terized by the frequent occurrence of yellow or orange pigment in 

 the adult, by the peculiar shape of the mesostigmal lamina, and the 

 structure of the nymphal abdomen and gills (p. 61). 



2. The civile-canmculatum group, containing civile, carunculatiim, double- 



dayi and possibly also calverti and cyathigerum, although the latter 

 may belong to another division (p. 65). 



3. The hageni-cbrium group, to which recurvatum, laterale and probably 



geminatum and minus ciiliiin also belong (p. 71). 



4. The exsidans-traviatwn group, composed of exsulans, traviuium and 



divagans and characterized by the color pattern of the thorax, which 

 shows a modified or divided stripe over the mesopleural suture, and 

 the peculiar shape and pigmentation of the gills of the nymph (p. 79). 



5. Durum apparently distinct from all other groups at least in the adult. 



6. Aspcrsum, possibly belonging to one of the other groups above but 



fairly distinct in the adult stage (p. 84). 



The different groups of Enallagmas are fairly distinct in habits, and 

 continued study of this phase of the question will reveal many more points 

 of difference than can be listed here. Thus group i is, in general, a small 

 clear-lake-loving group. Group 2 inhabits for the most part small ponds 

 and weedy pools, while group 3 is also a lake-pond group. The exsulans- 

 traviatum group are frequenters of small streams, usually slow flowing, but 

 are sometimes encountered in other localities. The only specimens of 

 group 5 that have been collected in Connecticut have been found near 

 brackish water, and it is probable that the species requires such an environ- 

 ment. The eggs of most species are laid on the stems of plants beneath 

 the surface, but this habit is not universal as indicated by the quotation 

 from Woods on page 14. 



Key to Species 



Nymphs' 



I. Gills without pigment except in tracheae and sometimes a trace 



along the axes 2 



Gills with pigment other than in tracheae, usually in cross-bands 7 



* This key is based primarily on the characters of the final stages with well-developed 

 wing-cases. The species hageni, ebriutn, geminatum. civile, and doubledayi are very 

 closely related and this part of the key should be used with caution. 



