214 



giving a detailed description. 



Described from materials obtained by D. K. McMillan at Lake 

 Forest, 111., November 29, 1916. 



The larva and pupa of this species were described by Needham 

 from this same locality, where they are abundant among algae on the 

 piers, just above and below the surface of the water. 



LiMNOBiA Meigen 



GENERIC CHARACTERS 



Larva. — Head broad, the exposed portion, except for the labrum, 

 subquadrate; antennae of moderate length, 2-jointed; mandibles 

 rather large. Body consisting of 12 segments; dorsal and ventral 

 surfaces with some or all of the segments individually armed with a 

 transverse band of setulae, those on ventral segments situated upon 

 more or less raised transverse ridges or swellings ; apical segment with 

 2 large, rounded spiracles, without well-defined tubercles, anal ventral 

 blood-gills short, consisting of a pair on each side. 



Pupa. — Head unarmed. Thoracic respiratory organs in the form 

 of a large disc-like chitinized plate which is attached, ear-like, to 

 anterior lateral angle of thorax ; legs elongated, the hind pair covered 

 almost to apex of basal tarsal joint by the wings, so that only 2 pairs 

 are visible for this distance, apices of tarsi almost in a straight line; 

 wings ending at apices of basal tarsal joints. Armature of abdominal 

 segments similar to that of larva except that the apical segment is 

 slightly chitinized and more or less tuberculate. 



I can not describe the position of the legs in either of the species 

 before me as only exuvia are available. The figure of hnmatnra is 

 made from a cast pupal skin, and details of the venter of the thorax 

 are incomplete. The spiracles on the abdomen are not well defined, 

 the normal chitinized margin of the openings, so evident in many 

 groups, being absent. In the specimens before me there are, how- 

 ever, two spiracles with distinct chitinized rims on the dorsum of the 

 eighth segment which are connected with stout tracheae. In the 

 specimen of immatura the main tracheae are still visible and each is 

 connected with the integument on the lateral margin of the segments. 

 The apices of the lateral branches appear to connect, by means of a 

 compact mass of thread-like branches, with the wall of the abdomen, 

 and have no distinguishable external aperture. Without a larger 

 amount of material for study I can not definitely state whether these 

 lateral tracheae are functional or not. 



