1939] 
Mosquitoes of Massachusetts 
117 
Eighth abdominal segment without an elongate single 
dorsal air tube; with a flattened spiracular disc on 
the eighth segment or with air sacs in the thorax and 
the seventh abdominal segment 3 
2. Antennse inserted close together, folding outwardly and 
fitting into grooves on the head (Fig. 20) : 
Corethrella 
Antennse inserted far apart, pendent in resting posi- 
tion (Fig 18) : Mochlonyx 
3. Air sacs present in thorax and seventh abdominal seg- 
ment (Fig. 17) : Chaoborus 
Air sacs absent, a well-developed spiracular disc on 
eighth abdominal segment (Fig. 19) : Eucorethra 
Key to the Genus Chaoborus 
Adults 
1. Wings spotted or clouded 2 
Wings without spots or clouds 4 
2. Width of hind marginal wing fringe nearly as great as 
distance between cubitus and hind margin__ ____3 
Hind marginal wing fringe less than half the distance 
between cubitus and hind margin : trivittatus 
3. Femora and tibiae with numerous distinct spots : 
punctipennis 
Femora and tibiae without distinct spots except at bases 
and apices: albatus 
4. Mesonotum with dark longitudinal bands : __ americanus 
Mesonotum with yellowish red longitudinal bands: 
albipes 
Larvae* 
1. Pre-labral leaf-like appendages very narrow and lan- 
ceolate : punctipennis 
Pre-labral leaf-like appendages less than seven times 
as long as broad 2 
2. Mandibular fan with 25 or more rays: americanus 
Mandibular fan with not over 18 rays 3 
3. Mandibular fan with 16-18 rays: trivittatus 
Mandibular fan with not more than 12 rays r.^albipes 
* Larva of C. albatus is unknown. 
