Carpenter et al.: Mosquitoes of Southern U. S. 41 



In addition to the labrum, the most prominent structures on the ventral side 

 of the head are the large maxillae, occasionally armed with characteristic spines, 

 and the heavily sclerotized mandibles, the teeth of which are used in conjunc- 

 tion with the sclerotized mentum for mastication. The labium forms the 

 remainder of the floor of the mouth and is composed of a proximal prementmn, 

 an intermediate mentum and a distal submentum. The shape of the mentum 

 and the size, shape and arrangement of its teeth provide useful diagnostic 

 characters in some species. 



The thorax consists of three completely fused segments, the pro-, meso-, 

 and metathorax, distinguished only by hair groups, particularly the pleurals, 

 which are present on each segment. 



The abdomen is made up of nme segments, the first seven of which are 

 somewhat similar. The eighth segment is modified to bear the breathing appa- 

 ratus postero-dorsally. The modification of this respiratory organ is one of the 

 most characteristic features in differentiating the larvae of Anophelines and 

 Culicines. The ninth (anal) segment bears several structures of taxonomic 

 importance, particularly in the identification of Culicines. 



The larvae of Culicines and Anophelines, while possessing many morpho- 

 logical features in common as stated above, differ in numerous obvious 

 respects. It is therefore convenient to discuss many of the diagnostic characters 

 separately. 



CULICINE larvae 



Important characters used in classifying fourth instar Culicine larvae are 

 shown in Figs. 17, 18. The terminology used here follows that employed by 

 Hopkins (81), with modifications. 



HEAD. (Fig. 18). — Each antenna is an elongate, cylindrical structure, gener- 

 ally curved inward. It bears an antennal tuft (often a single small hair) on 

 the inner surface, and a pair of strong subterminal spines near the apex. A pair 

 of strong terminal spines and a membranous papilla are located at the apex of 

 the antenna. The principal taxonomic features of the antenna are its length, 

 shape, the presence or absence of small spines on the shaft, and the position 

 and nature of the antennal tuft. 



The paired hairs of the head capsule commonly considered in specific 

 descriptions are as follows: Preantennal (A), lower head hairs (B), upper 

 head hairs (C), postclypeal hairs (d), suturals (e), trans-suturals (f), supra- 

 orbitals, basals and sub-basals. The position of these hairs, their size, and 

 number of branches may vary greatly in the different genera and species. 



THORAX. — The pleural hair groups (propleural, mesopleural and meta- 

 pleural) are indicators of the segmentation of the thorax. The dorsal submedian 

 prothoracic hairs (1-3) are useful in separating the two species of Uranotaenia 

 occurring in this region (Figs. 52, 54). The lateral hairs (5-7) are of diagnos- 

 tic value in separating Mansonia indubitans and M. titillans. The other hair 

 groups of the thorax are seldom used in the classification of the Culicines. 



