THE EARLY STAGES OF CERTAIN WEST AFRICAN MOSQUTTOS. 149 



difference in the length of the anal papillae or " tracheal gills" could be detected 

 between the larvae found in the brackish and the fresh water. 



The larvae were commonly found together with larvae of A. costnlis and occasionally 

 with those of 0. minutus, 0. otocephalus, C. invidiosus, C. tritaeniorhynchus, and 

 C. fatigans. Larvae of C. tigripes var. fuscus were found preying upon them. 



The imago is one of the most troublesome mosquitos in the bungalows at Accra 

 and is a severe biter. 



Culex tritaeniorhynchus, Giles. 



This larva, which occurs in the same pools as the larva of C. invidiosus, resembles 

 it closely in configuration. When the two larvae are examined side by side, however, 

 that of C. tritaeniorhynchus seems to be more robust, to have a longer siphon and to be 

 more strongly chitinised. 



The head is large, almost as wide as the thorax. The antenna is covered with 

 spicules, and its outer third beyond the insertion of the hair-tuft is much darker and 

 has more prominent spicules than the basal two-thirds. The tuft of very plumose 

 hairs is placed at two-thirds of the length of the antenna from its base. The mouth- 

 brushes are prominent. The mid-frontal hairs are plumose, and the ante-antennal 

 tuft is formed of dark and plumose hairs rising from a pedicle. The eyes are large. 

 The mental plate shows a moderate-sized median tooth with 6-8 pointed teeth on 

 either side, its posterior border being deeply incised mesially. The mandibular teeth 

 are more powerfully developed than those of C. invidiosus. 



The thorax carries the usual long plumes. The lateral abdominal hairs are sub- 

 plumose and are multiple on the first segment, triple on the second segment and paired 

 on the remaining segments. All the abdominal segments show stellate hairs, which 

 are longer than the similar and similarly placed hairs on the abdomen of the larva of 

 C. invidiosus. The comb comprises 35-40 fringed scales, which appear to be darker 

 than the comb-scales of C. invidiosus. The siphonal and subsiphonal plumes are 

 formed of plumose hairs, the hairs of the anal plume being simple. The siphon is 

 about ten times as long as the diameter of its base ; there are 10-12 spines, wmich 

 are barbed inf eriorly, in the pecten. The siphon also carries 6-8 pairs of tufts of simple 

 hairs distally to the pecten ; these tufts are longer than the tufts on the siphon of 

 C. invidiosus, and those visible vent-rally are more regularly placed in line. The anal 

 segment is almost as wide as it is long (23 units : 21) ; the anal papillae are equal, 

 have pointed ends, and are longer than the anal segment. The beard is fairly 

 developed, and the dorsal hairs on this segment resemble the similar hairs on the 

 anal segment of C. invidiosus. 



This larva, as stated above, bears a striking resemblance to the larva of C. invidiosus, 

 the apparently distinctive points have been tabulated below : — 



C. tritaeniorhynchus. C. invidiosus. 



Larva as a whole . . More robust. Less robust. 



Antenna . . . . Apical portion above origin Apical portion scarcely 



of hair-tuft darker and darker, spicules not more 



with more prominent spi- prominent, 

 cules. 



