808 CHARLES PAUL ALEXANDER 



Labium strongly chitinized, triangular, split longitudinally. Mandible (Plate XXIII, 75) 

 clawlike in appearance, a little smaller than either half of labium, on inner face with a chiti- 

 nized projection which is serrated. Maxilla indistinct, the palpi coroniform. Spiracular disk 

 (Plate XXIII, 77) with four lobes whose inner faces are narrowly lined with black chitin; 

 lobes provided with lashes of long gray hairs; dorsal lobes the shorter and broader, and bear- 

 ing on their inner face two elongated stigmata which are margined with pale rust-yellow. 



Pupa.' Length, 6.5 mm. 



Pronotal breathing horns (Plate XXIII, 76) large, ear-shaped; bright yellowish white in 

 color, in contrast to dirty yellowish brown skin of head, thorax, and appendages; each horn 

 consisting of two parts: the dorsal side, appearing smooth and homogeneous; and the ventral 

 side, with two longitudinal furrows converging toward apices, and with abundant elongate 

 tubercles, under low magnification this part appearing pitted because of the spaces between 

 these tubercles. Margin of breathing horn chitinized and very finely notched. On outer 

 basal part of each ear a parchment-like lobe, which joins ear to side of prothorax; in addition 

 to this, each ear at base is drawn out into an almost rectangular lobe which is closely approxi- 

 mated to pronotum. Leg sheaths extending about to base of fifth abdominal segment. 

 Abdomen distinctly depressed, greenish white in color; segments 3 to 7 on both dorsum and 

 sternum near base with a double cross-row of spicules which present a comblike appearance 

 (Plate XXIII, 78), those on dorsal segments being somewhat stronger. Female pupa with 

 acidothecae grown together on inner face, at outer angle of each a chitinized hook which is 

 curved upward. Male pupa with ventral side of last segment produced into two chitinized 

 points which are bent toward each other and almost touch, these inclosing clasping organs 

 of adult male and hooks of male larva as described above. 



Subtribe Limnobaria 



The subtribe Limnobaria includes about ten genera, which are very 

 closely related to one another and whose limits are as yet not clearly 

 defined. Many of the generic distinctions are based on male characters 

 of wing form, venation, or antennal structure. The genera are often very 

 large and it is difficult to give satisfactory characters to separate their 

 immature stages. The keys to the genera, given below, will unquestion- 

 ably need much revising when a larger number of forms are studied. 



Larvae 



1. Form stout; teeth of mandibles and of mentum usually more numerous; mentum more 



pointed anteriorly Limnobia Meig. (p. 809) 



Form usually more slender; teeth of mandibles and of mentum usually fewer; mentum 

 transverse or subtransverse 2 



2. Mandibles very broad, flattened, with three ventral cutting teeth; mentum about trans- 



verse, with nine or eleven teeth Rhipidia Meig. (p. 825) 



Mandibles more slender, with usually four or five cutting teeth; mentum usually a little 

 pointed anteriorly, with about eleven teeth Dicranomyia Steph. (p. 819) 



