283 



which are represented in fi^i^ures 7 and 8, Plate XXIII. The hibruin 

 hangs over in front of the head, and can be drawn backward so as to 

 close over the mouth orifice. The function of the hooks present on the 

 cpipJiarynx, or under surface of the labrum, is i)robably that of retain- 

 ing food in the mouth, but they are also used in assisting the larva in 

 its movements \vithin its burrow, and also over any surface, as in pro- 

 gressing it generally grasps the sides of the burrow or some other ob- 

 ject with the mouth parts, drawing the body forward at the same time. 

 To the lateral plates are attached the autcniur and inandiblcs ; on each 

 lateral plate there are generally two black pigment spots, wdiich are ru- 

 dimentary eyes; the lateral plates curve down over the side of the head 

 and meet in the center of the under surface, which junction is marked 

 by a faint suture. The aiifciiiuc are in many larvre very small, in others 

 of considerable size, and in Tanypus and its allies are retractile within 

 the head for almost their entire length. The usual form of antenna 

 consists of a large and stout basal joint, on which there is generallv a 

 sensory spot, or a hair, and on the apex of this joint one simple, gen- 

 erally hairlike, process of varying length, and a process with three to 

 five distinct joints, which presumably represents the true continuitv of 

 the antenna. The inandiblcs in all the species which I have examined 

 are large and heavily chitinized, generally toothed on their inner sur- 

 face, and move on an articulated l)ase so as to close inward ; when com- 

 pletely closed their apices are visible behind the anterior transverse 

 margin of the labial plate. The brushlike hairs which are present on 

 the mandibles of the larvae of Siimdidcu and Ciilicidcc are much less 

 prominent in the larvai of CJiironoiuidcc, though still distinguishable. 

 The maxiUcr are much retracted and rather rudimentary in many spe- 

 cies, and but little use has been made of them in descriptions. The 

 character which has been used more than any other for the separation 

 of larvae of this family lies in the structure of the labiid plate, or snb- 

 mentnni. In Chirouonius and several other genera, OrtJwcladius and 

 Cricotopus in particular, this plate -is exposed and is therefore easily 

 accessible; but in all the species of Tanypincc which are represented in 

 the material before me, the labial plate is very small and generally re- 

 tracted within the mouth, or occupies a vertical position so that its 

 form is indistinguishable; the labial papilla: of a species of CJiirononuis 

 are as in Figure 10, Plate XXIII. A further discussion of this matter 

 will be found under Tanypincc. The larval head of Dixa differs very 

 considerably from that of any chironomid, and shows the dorsal 

 sclerites clearly (PI. XXIII, Figs. 9 and 12). 



Abdomen. — The thorax and abdomen of the larva combined con- 

 sist of twelve segments, which are almost devoid of hairs in most of 

 the aquatic species. Several of the terrestrial species cire figured here- 



