130 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I25 



Larva (pi. 40, fig. 363, and pi. 42, fig. 400). — Total length, 5.7-6.1 

 mm. Width of head capsule equal to the length. Width of thorax 1.6 

 times that of head. Width of first four abdominal segments 1.2 times 

 that of head ; segments 5-7 expanded, greatest at segment 6 which is 

 1.4 times width of segments 1-4 ; cross section and general shape equal 

 to that of larvae in the subgenus Simulium. General color smoke gray 

 with slight green coloration in some regions ; black patches on ventro- 

 lateral regions of segments 6 and 7 present, but not very distinctly 

 marked. 



Head: Designs on frons-clypeus and epicranial plates shown on 

 plate 40, figure 363. Each cephalic fan with 30-32 pectinate branches, 

 the hairs on these branches short, heavy, close together, with some- 

 what longer, bifid hairs interspersed at regular intervals. Mandible 

 with 2 flattened teeth on its inner margin that appear to arise as 

 branches from the same base ; apical tooth much longer and broader 

 than the other. Antenna 400 fi long, 4-segmented, just surpassing the 

 basal stalk of cephalic fan ; segments 1-3 subequal in length ; seg- 

 ments I and 2 dark brown, 3 and 4 lighter in color ; segment i with 

 longitudinal striations. Submentum with 9 apical teeth, shaped like 

 half of a hexagon, the central tooth and the outermost tooth on either 

 side larger than the others ; ventrolateral row composed of 7 hairs in 

 straight line, the hairs bifid and trifid ; lateral margin of submentum 

 serrated, with about 8 toothlike processes. Occipital cleft deep, dome- 

 shaped, the apex pointed (pi. 42, fig. 400). 



Thorax and Abdomen : Pseudopod (thoracic proleg) with 38-42 

 rows of hooks at its apex ; postclypeal sclerites small, but well sclero- 

 tized. Posterior sucker with 105 rows of hooks. Anal gills with 3 

 main divisions each with usually 5 fingerlike processes, some longer 

 than others ; at times, there are as many as 24 processes in all, the 

 central division on such specimens having 14 ; the lateral divisions 

 may have up to 7 processes. Anterior and posterior arms of X-shaped 

 sclerite heavily sclerotized, the anterior arms short and completely 

 obscured by wedge-shaped patches that start at the union with the 

 posterior arms ; patches much larger than on downsi; approximately 

 10 rows of rectal scales, posteriorly directed, each with from 1-5 

 denticles at tip ; small, round protuberance on either side, just posterior 

 to anal opening and lateral to it, covered with numerous spines ; row 

 of simple spines behind each posterior arm. Two extremely small 

 ventral papillae on eighth segment, hardly visible ; no plaques. 



Types.— 2 (U.S.N.M. No. 28667) in the collection of the United 

 States National Museum ; collected in Cordoba, Veracruz, Mexico. 



